Chapter XXIII: Appendix: I

NOTE ON THE CARTOGRAPHICAL RESULTS OF HASSANEIN BEY’S JOURNEY

John Ball, O.B.E., D.SC., Director of Desert Surveys, Egypt

=1. Introduction=

THE cartographical data brought back by Hassanein Bey consist of:

(1) Note-books containing the records of astronomical observations for the determination of time, latitude, and compass-variation at nineteen principal camps, with records of watch-comparisons.

(2) A journal giving a continuous record of observed compass-bearings and estimated distances from Siwa Oasis to Lameina Wells, near El Fasher, a distance of about 2430 kilometers.

The journal also contains a considerable number of observed compass-bearings to conspicuous features on either side of the route, with a few rough trigonometrical estimations of the altitudes of mountains passed, a large number of readings of an aneroid barometer and sling thermometer for the estimation of altitudes along the route, daily observations of maximum and minimum temperatures, observations on the character of the country passed through, and notes on the meteorological conditions.

These observational data have been reduced in the Desert Survey Office, Cairo, and utilized in the preparation of the map on a scale of 1:2,000,000 which accompanies Hassanein Bey’s account of his travels. The objects of the present note are, first, to give an account of the critical examination to which the records were subjected in the course of the reduction of the observations, so as to enable an estimate to be formed of the degree of precision which may be fairly assigned to the geographical positions, altitudes, and other results used in the construction of the map; and, secondly, to indicate the additions to existing geographical knowledge concerning a little-known region of northeast Africa which have accrued from the expedition.

=2. Astronomical Determination of Local Time=

Theodolite observations of altitudes of the sun or of stars were made at all the principal camps for determining the error on local mean time of the half-chronometer watch which was used in the latitude observations. In all, thirty-four complete time determinations were made at seventeen camps. The observations were made with a three-inch Troughton & Simms theodolite, the vertical circle of which could be read by two verniers to 1′, and which was provided with a sensitive level on the microscope arm. The theodolite was invariably set up in the magnetic meridian by its trough compass, and the method used was to note the times of passage of the sun’s limb or of the star over each of the three horizontal wires of the stadia-graticule, reading the level and circle at each pointing, face-right and face-left. In the case of stars, the magnetic bearing of the star was also noted from the horizontal circle, and a note made of the color and brightness of the star, for the identification of the stars subsequently in the office, and thus to free the observer from the necessity of knowing the stars’ names. The barometer and thermometer were carefully read at each observation for calculating the refraction.

No difficulty was experienced in subsequently identifying the stars. In only a single case was it found necessary to reject an observation, and this because the observer had accidentally sighted different stars on the two faces of the instrument. On many days two or more observations were taken at the same place, and comparisons of the results at these places indicated that the observations are remarkably accurate for so small an instrument. In seven cases where the sun has been observed shortly before sunset and a star soon after sunset, for example, the maximum difference between the results given by the two observations is only seven seconds, while the average is under four seconds. It is thus apparent that the precision of the time observations is amply sufficient to insure that no sensible error in the latitudes can be due to errors of the adopted local times.

As the only use made of the time observations in the preparation of the map has been in the determination of latitude, it would serve no useful purpose to give a list of the watch errors. But it may interest future geographers, undertaking long desert journeys, to note some of Hassanein Bey’s experiences in the transport of watches, and the hazard of relying on constancy of rate for long periods with even the best watch.

Of the six watches carried, only a single one remained in going order throughout the journey. The timekeeper which thus successfully resisted the vicissitudes of the seven months of desert travel was fortunately the one with which Hassanein Bey took all his observations, and was carried in his pocket during the entire journey; it was a large-sized half-chronometer “explorer’s” watch of English manufacture, with a dust-proof cap to the winding mechanism. It had been awarded an “especially good” certificate at the National Physical Laboratory of England, and was consequently the most expensive of all the six watches taken on the journey. Even this watch failed to maintain a sufficiently constant rate to be of any service in the determination of longitudes, though it amply sufficed for the latitudes, even in two cases when reliance had to be placed on the constancy of its rate for one or two days owing to latitude alone being observed without corresponding observations for local time. Thus, for instance, the following were the average rates of the principal watch deduced from local time observations at places of previously known latitudes:

RATE OF PRINCIPAL WATCH

Sollum to Siwa Dec. 29-Jan. 13 15 days losing 5.8 secs.

Siwa to Jaghbub Jan. 13-Jan. 20 7 “ “ 0.1 “

Jaghbub to Furawia Feb. 14-June 5 111 “ “ 7.7 “

Furawia to Um Buru June 5-June 8 3 “ “ 6.6 “

Um Buru to El June 8-June 26 18 “ “ 9.4 “
Fasher

El Fasher to El June 30-July 15 15 “ “ 9.4 “
Obeid

The above table fails, however, to bring out fully the actual variations of the watch. So long as the other five watches remained in order, Hassanein Bey made frequent comparisons with his principal watch, and between March 21 and 23 there is strong evidence that the principal watch made an abnormal gain of about fifty seconds. A similar abnormal gain of twenty-nine seconds by the principal watch is evidenced in the twenty-four hours between comparisons of March 24 and 25. Both these abnormalities occurred between Jalo and El Harrash, at an early stage of the journey, while all the watches appeared to be behaving tolerably well, and it is quite possible that other abnormalities occurred at later stages, when, owing to some or all of the other watches having stopped or broken down, no satisfactory control by comparison was possible.

Of the other five watches carried, one was an English half-chronometer, similar to the principal watch but of smaller size; three were high-class Swiss lever (“Peerless”) watches with very tight-fitting cases; and the fifth was a small Swiss lever-watch with luminous dial, carried on the wrist for noting the times of marching. The small half-chronometer stopped on April 3, after going for over four months; and though it was restarted, its rate changed considerably after the stoppage. The three “Peerless” watches, though they failed to continue going to the end of the journey, showed by no means a bad record. One was found stopping and unreliable on May 6, after going for over five months; the two others continued to go for over a month longer; and so far as can be judged from the comparisons made on the route, their variations of rate were about of the same order as those of the half-chronometers. The wrist-watch, from the manner in which it was carried, was of course liable to much greater variations of rate, and was occasionally reset by the principal watch; but it kept going till nearly the end of the journey.

As regards dust-resisting power, which must always be one of the principal aims in selection of watches for desert exploration, there appears to be nothing to choose between good English half-chronometers and the highest class of Swiss watches, the cases of the latter being remarkably close-fitting. The most probable cause either of stoppage or of abnormal changes of rate appears to be the sudden shocks which may arise either to a watch carried on the person when jumping on or off a camel, or to one carried in the baggage by sudden movements of the camel. The most likely explanation of the abnormal gains of the principal watch for short periods on the two occasions above noted would seem to be that, owing to a jerk in mounting or dismounting, two contiguous coils of the hair-spring may have been made to touch each other for a short time, with consequent temporary shortening of the period of vibration of the balance-wheel. It is noteworthy that the watch which remained going throughout the journey was the largest of all those taken, and its greater resisting-power may have been to some extent due to its size, permitting of greater strength in its component parts.

=3. Astronomical Determinations of Latitude=

Observations for latitude by altitudes of the pole-star were carried out on thirty-five nights at nineteen principal camps, using the same three-inch theodolite as was employed for the time-observations. Three readings of altitude were made on each face, using each of the three horizontal stadia-wires in turn, the corresponding times being noted on a half-chronometer watch whose error on local time was accurately known from sun or star-observations carried out just before the latitude-observation. Particular care was taken with the level-adjustment, and the air-pressure and temperature at the time of the observation were recorded.

The following table gives the results of the observations:

ASTRONOMICAL LATITUDES

° ′ ″

Sollum 4 nights Lat. 31 35 9 N.

Siwa 1 “ “ 29 12 41 “

Jaghbub 5 “ “ 29 44 26 “

Camp near Jalo 1 “ “ 29 11 56 “

Jalo (El Erg) 1 “ “ 29 2 33 “

Buttafal 1 “ “ 28 54 26 “

El Harrash 1 “ “ 25 26 29 “

Taj 6 “ “ 24 13 47 “

Arkenu 2 “ “ 22 12 32 “

Ouenat 1 “ “ 21 52 29 “

Erdi 1 “ “ 18 35 39 “

Agah 1 “ “ 17 52 38 “

Enebah 1 “ “ 17 21 24 “

Bao 1 “ “ 16 28 24 “

Furawia 2 “ “ 15 21 51 “

Um Buru 2 “ “ 15 3 57 “

Kuttum 1 “ “ 14 12 15 “

El Fasher 2 “ “ 13 38 3 “

El Obeid 1 “ “ 13 10 51 “

Of six of the above places (Sollum, Siwa, Jaghbub, Kuttum, El Fasher, and El Obeid) the latitudes are accurately known from the Egyptian and Sudan official surveys, and the agreement in these cases is very satisfactory, though a very close comparison is not generally possible owing to uncertainty as to Hassanein Bey’s precise observation-spot. At Jaghbub, Hassanein Bey records that his observation-spot was 200 meters S.S.W. of the dome of the mosque. Applying the corresponding difference of latitude (− 6″) to my own determination of the latitude of the dome in 1917 (29° 44′ 41″) we obtain 29° 44′ 35″, showing a difference of only 9″ from Hassanein Bey’s observed latitude.

A further test of the degree of precision of the latitude-observations can be made by comparison of the latitudes found for the same camp by observations taken on different nights. The following gives the average deviation of a single observed latitude from the mean at all the camps where two or more observations for latitude were made:

″

Sollum 4 nights Av. dev. 8

Jaghbub 5 “ “ 40

Taj 6 “ “ 12

Arkenu 2 “ “ 6

Furawia 2 “ “ 8

Um Buru 2 “ “ 23

El Fasher 2 “ “ 6

It thus appears unlikely that any observed latitude can be as much as 1′ in error, and consequently in the preparation of the map, Hassanein Bey’s observed latitudes have been accepted as fundamental data for all the places for which no previous determinations are known to exist, viz., El Harrash, Taj, Arkenu, Ouenat, Erdi, Agah, Enebah, and Bao. His latitudes for Jalo (El Erg), Bir Buttafal, and Furawia have also been adopted for the map, the first because it is possibly better than that of Rohlfs, with whose mapped position it is however in very close agreement; the second because while differing by about 2′ from Rohlfs’s value (28° 36′ 22″) it is doubtless more exact, because it checks admirably well with Hassanein Bey’s dead reckoning; and the third because, although the position of Furawia is shown on the Sudan maps, it is outside the present limits of the Sudan triangulation and is possibly liable to some slight error.[1]

=4. Observations of Compass-Variations=

For finding the pole-star easily when the sky was not very dark or was partially obscured by clouds, and also for obtaining the approximate bearings of time-stars for their subsequent identification, the theodolite was invariably set up in the magnetic meridian by its trough-compass, and the magnetic bearing of the pole-star was read on the horizontal circle after each latitude-observation and the time noted. In this way approximate compass-variation was determined at each camp, with the following results:

VARIATION OF THE COMPASS

° ′

Sollum Dec., 1922 3 obs. 2 34 W.

Siwa Jan., 1923 1 “ 2 42 “

Jaghbub Feb., 1923 5 “ 2 25 “

Near Jalo March, 1923 1 “ 4 12 “

Jalo (El Erg) “ “ 1 “ 4 5 “

Buttafal “ “ 1 “ —

El Harrash “ “ 1 “ 3 48 “

Taj April, 1923 6 “ 3 32 “

Arkenu “ “ 2 “ 3 25 “

Ouenat “ “ 1 “ 3 32 “

Erdi May, 1923 1 “ 3 57 “

Agah “ “ 1 “ 4 0 “

Enebah “ “ 1 “ 4 21 “

Bao “ “ 1 “ 4 59 “

Furawia June, 1923 2 “ 4 32 “

Um Buru “ “ 2 “ 3 25 “

Kuttum “ “ 1 “ 4 26 “

El Fasher “ “ 2 “ 2 51 “

The method of estimating the compass-variation with the theodolite is, of course, only rough; but the values found are probably correct at most places within half a degree, and they serve to show that there is no likelihood of any serious errors of dead-reckoning owing to local irregularities of the compass-variation. They have accordingly been utilized in reduction of the compass-bearings of the traverse to true bearings over the major portion of the route, where no previous determinations exist, and where in consequence the distribution of the isogonic lines is not known with any exactitude.

=5. Longitudes=

The probability of some watches breaking in the course of seven months’ travel had been foreseen, and from the outset it appeared improbable that any use could be made of the watches in the direct determination of longitude of so long and difficult a journey. We had decided accordingly to depend ultimately on dead-reckoning for longitude, making every effort to obtain an unbroken chain of compass-bearings and estimated distances between Jaghbub and some known place in the Sudan, the bearings to be taken with a good compass with all possible precision, at very frequent intervals, and the estimates of distance to be carefully made each day from the marching time of the baggage-camels, assuming a normal rate of 4 km. per hour over average desert, and making allowance for the variations in speed over ground of varying character. The journey being predominantly north to south, the estimates of distance could mostly be well controlled by the latitudes, while errors of bearing would not be cumulative, and would tend to cancel out over any considerable stretch of route. The primary reason for taking six watches was therefore not to determine longitude, for which at best they could afford only somewhat uncertain values, but to make sure of at least one watch being available throughout the journey for latitude-observations, without which no proper control of the all-important distances could be obtained.

The doubts about the possibility of safely transporting the watches proved justified, for all but one broke down before the end of the journey. But fortunately on the one hand the watch which survived sufficed amply for the determination of latitude (though its rate was insufficiently constant for it to be used uncontrolled in finding longitudes), and on the other hand the program of a continuous chain of very careful bearings and estimation of distances was scrupulously adhered to from the departure of the caravan from Jaghbub, the last known place in Egypt, to Furawia, the first known place in the Sudan—a journey of 2430 kilometers—and from this chain of bearings and estimated distances, combined with the observed latitudes, it was possible to estimate the longitudes of all places on the route with a fairly high probability of accuracy.

For the estimation of the longitude of Jalo (El Erg) a slightly different procedure was followed from that adopted for the other principal camps on the route. It will be noticed from the map that the general direction of the march from Jaghbub to Jalo was predominantly from east to west, instead of from north to south as in the rest of the journey. Consequently the observed latitudes do not afford so good a means of correcting the estimated distances in this stretch as elsewhere. But fortunately the observed latitude at Jalo does enable us to correct the previous estimation by Hassanein Bey (in 1920) of the distance of that place from Jedabia, and this combined with the then observed bearings would lead to one value for the longitude for Jalo, while if we can assume the accuracy of the estimated distances from Jaghbub to Jalo, we may use the observed latitude of the latter place to correct the bearings and thus arrive at another value for its longitude.

From careful consideration of all the available data, the two methods appear likely to be about equal in degree of approximation. The position at present accepted for Jedabia (Lat. 30° 48′ 10″ N., Long. 20° 13′ 30″ E.) is open to a little uncertainty,[2] and the bearings taken by Hassanein Bey on his former expedition are probably a little less accurate than those of the present one. On the other hand, the estimations of the distances from Jaghbub to Jalo, as gaged by the latitude-control of the other portions of the route of the present expedition, are remarkably close to the truth, while a uniform correction to his bearings of less than half a degree would swing his dead-reckoning position for Jalo on to its observed parallel of latitude.

For the longitude of Jalo on the map I have therefore taken the mean of the two longitudes found (1) by assuming Hassanein Bey’s bearings correct from Jedabia and correcting his distances by the latitudes, and (2) by assuming his distances from Jaghbub correct and using the observed latitudes to correct his bearings. The results are:

° ′ ″

(1) From Jedabia, long. of Jalo (El Erg) 21 29 48

(2) From Jaghbub “ “ “ 21 26 19
--------
Adopted mean 21 28 3

It may be remarked in passing that the result places Jalo almost precisely where it is shown on Rohlfs’s map of 1880.

As regards the longitudes adopted for the other principal camps along the route, the procedure has been as follows. The route was divided into the following nine sections between principal camps where latitudes had been observed: Jalo, El Harrash, Taj, Arkenu, Ouenat, Erdi, Agah, Enebah, Bao, Furawia; and the compass-traverse for each section was plotted on a scale of 1:500,000 from the recorded bearings and estimated distances. A true meridian was then drawn on each section from the mean of the observed compass-variations at its two ends, and the total difference of latitude of each section was scaled off and compared with the difference of latitude given by the latitude-observations. This comparison gave, of course, the average error of estimation of distance along each section, assuming the bearings correct. The results of the comparison for the various sections are tabulated below:

CORRECTION TO ESTIMATED DISTANCES

_True _Correction
_Plotted difference _True- to
_Section of difference from plotted estimated
traverse_ of latitude_ latitude- diff. lat._ distances_
observations_

km. km. km. %

Jalo-El 375.0 399.0 + 24.0 + 6.4
Harrash

El Harrash-Taj 131.5 134.2 + 2.7 + 2.1

Taj-Arkenu 217.7 223.7 + 6.0 + 2.8

Arkenu-Ouenat 36.0 37.0 + 1.0 + 2.8

Ouenat-Erdi 369.0 363.2 − 5.8 − 1.6

Erdi-Agah 75.6 79.2 + 3.6 + 4.8

Agah-Enebah 57.0 57.5 + 0.5 + 0.9

Enebah-Bao 99.0 97.7 − 1.3 − 1.3
-----
Mean error of estimation of distances, per cent 2.6

The average error of distance-estimation in each section of the route having been thus found, the next step was to scale off the various departures from the plotted traverses, correcting for the errors of distance-estimation, and then to convert the departures into differences of longitude. When this was done, the resulting total difference of longitude between Jalo and Furawia was 2° 25′ 55″. But assuming the true longitude of Jalo to be that found above, and the true longitude of Furawia to be as shown on sheet 53 D of the 1:250,000 Sudan survey map of 1921,[3] we have:

° ′ ″

Longitude of Jalo 21 28 3

Longitude of Furawia 23 38 10
------------
Difference 2 10 7

So that the difference of longitude found by the dead-reckoning requires correction by 15′ 48″. This correction, which implies an average error in the observed compass-bearings of less than a degree, and a negligible correction to the adjusted distances, was distributed along the entire traverse in proportion to the difference of latitude between the principal camps, leading to the finally adopted longitudes shown in the following table:

CONCLUDED LONGITUDES

_Dead-reckoning _Further _Concluded
corrected by correction_ longitude_
the latitudes_

° ′ ″ ′ ″ ° ′ ″

Jalo — — 21 28 3 E.

El Harrash 22 15 5 E. 4 10 22 10 55 “

Taj 23 29 5 “ 5 34 23 23 41 “

Arkenu 24 52 10 “ 7 55 24 44 15 “

Ouenat 25 2 34 “ 8 18 24 54 16 “

Erdi 23 22 34 “ 12 5 23 10 29 “

Agah 23 28 49 “ 12 54 23 15 55 “

Enebah 23 25 58 “ 13 30 23 14 28 “

Bao 23 16 18 “ 14 31 23 1 47 “

Furawia 23 53 58 “ 15 48 23 38 10 “

In attempting to estimate the probable degree of accuracy of the concluded longitudes, we are faced with the difficulty that while we may be certain that the _average_ error of the compass-bearings was less than 1°, which average error has been allowed for in the adjustment, we have no proof that in some of the individual sections the errors may not have been considerably greater. But in view of the great number of the observed compass-bearings (339) which make up the directional data of the 1754 kilometers of traverse from Jalo to Furawia (an average of thirty-eight observed bearings for each of the nine sections), and bearing in mind also the remarkable accuracy of the estimations of distance as evidenced by the latitude-observations, it would seem unlikely that any of the above-adopted longitudes for the principal camps can be in error by more than three or four miles. This implies a degree of accuracy which it would have been difficult to insure by transport of even a considerable number of chronometers over a land journey lasting more than three months. It may, I think, be concluded that no better values for the longitudes can be obtained without the aid of wireless time-signals.

=6. Altitudes above Sea-level=

For the barometric estimations of altitudes above sea-level, a two-inch aneroid by Steward was used. This instrument, which was one of two specially made for the expedition, was very carefully compensated for temperature, and provided with a fairly open pressure-scale, a millimeter of pressure being represented by very nearly a millimeter of actual scale-length, so that estimations to half-millimeters of pressure could be readily made.

The aneroid was read morning and evening at each camp, and at numerous other points on the route, the air-temperatures being as a rule recorded at the same time, as given by sling-thermometer. The aneroid behaved very satisfactorily throughout the journey. There had unfortunately been no opportunity of testing the instrument before Hassanein Bey’s departure, but it was in perfect order on his return, and was then tested in the laboratory of the Physical Department at Cairo, when it was found to require the following corrections (at about 25° C.):

Pressure, mm. 760 750 740 730 720 710 700 690

Correction, mm. − 2.3 − 2.3 − 2.3 − 2.1 − 1.4 − 1.1 − 0.1 + 0.6

[Continued]

Pressure, mm. 680 670 660 650

Correction, mm. + 1.7 + 2.0 + 2.8 + 2.9

That the above corrections had remained sensibly constant throughout the journey is rendered extremely probable by the close agreement noted further on (p. 329) between the levels found for Jalo directly from the aneroid readings (corrected, of course, on the assumption of constancy of the table) and those found indirectly from readings of the mercurial barometer in the meteorological station at Siwa.

The first step in the calculation of the barometric levels was to collect the whole of the readings of the barometer and sling-thermometer at each of the nine principal camps, where a halt of at least several days had been made, and a considerable number of readings taken. The means of all the recorded pressures and air-temperatures were taken for each of these principal camps, and the pressure corrected for instrumental error from the table above given. The readings being taken at various times of the day, the diurnal variation of pressure could safely be neglected, as it would most probably disappear on taking the mean of the readings. To allow for the annual variation, the mean pressures were next reduced to the mean of the year by applying a correction based on the mean of the normal annual variations at Siwa and El Obeid, as found from the recent volume of “Climatological Normals” issued by the Physical Department of Egypt and shown in the following table:

CORRECTIONS TO REDUCE MONTHLY MEAN PRESSURES TO ANNUAL MEANS

_Jan._ _Feb._ _March_ _April_ _May_ _June_ _July_

mm. mm. mm. mm. mm. mm. mm.

Siwa − 3.4 − 2.0 − 1.9 + 0.9 + 0.9 + 2.7 + 3.5

El Obeid − 1.2 + 0.7 + 0.3 + 1.2 + 1.0 + 0.6 0.0
----- ----- ----- ----- ----- ----- -----
Mean − 2.3 − 1.4 − 0.8 + 1.0 + 1.0 + 1.6 + 1.8

A further correction to allow for the distribution of the sea-level isobars over the region traversed was desirable, but no sufficient data exist for estimating its amount; the distribution is, however, probably nearly linear, and such a distribution was approximately allowed for by assuming the previously accepted levels at Siwa (− 17 m.) and El Fasher (793 m.) to be correct and distributing any residual difference found by the otherwise corrected barometer readings between these two places uniformly among the different sections.

The difference of height corresponding to each difference of mean corrected barometer-readings was calculated by the tables of _Barometrische Höhenstufen_ in Jordan’s “Mathematische und Geodätische Hülfstafeln,” for the air-temperature corresponding to the mean of the thermometer-readings at the two ends of the line.

The adopted levels of thirteen principal camps as found in the above manner are tabulated below. It is interesting to note that the residual difference of height which had to be distributed between Siwa and El Fasher, and which is presumably mainly due to systematic pressure-gradient, was sixty-three meters, corresponding to a normal fall of sea-level pressure between the two places of about 5 mm., and this is from other considerations probably very near the truth; also that the resulting adjustment which had to be made in the levels in any single main section of the route did not exceed five meters.

CONCLUDED ALTITUDES ABOVE SEA

_Diff.
_Number _Mean _Mean of _Diff. _Altitude
of pressure tempera- height of above
obser- (correct- ture_ from height sea-
vations_ ed)_ Jordan’s (adjust- level_
tables_ ed)_

mm. ° C. meters meters meters

Siwa 4 762.6 12 — — − 17

Jaghbub 50 757.7 15 + 54 + 49 + 32

Jalo 18 754.7 17 + 34 + 29 61

El Harrash 6 732.8 23 + 254 + 249 310

Taj 31 718.5 19 + 170 + 165 475

Arkenu 12 708.0 31 + 128 + 123 598

Ouenat 14 706.3 31 + 21 + 18 616

Erdi 7 683.3 31 + 295 + 290 906

Agah 3 695.2 34 − 157 − 162 744

Bao 5 677.7 33 + 230 + 225 969

Furawia 11 685.8 31 − 107 − 112 857

Um Buru 8 679.5 30 + 83 + 78 935

Kuttum 5 660.2 24 + 254 + 249 1184

El Fasher 5 689.7 31 − 386 − 391 793

After thus determining the levels for the principal camps, those of intermediate camps and other places were computed in a similar manner, adjusting each section to the adopted levels at its terminal points. The maximum adjustment which it was found necessary to apply to the difference of height given by the barometer between points a day’s journey apart was five meters, and the average three meters.

An exception was made in the stretch between Jaghbub and Jalo, where no intermediate levels were adopted for the map, owing to the extremely unstable state of the atmosphere during the journey between these two places; sand-storms of great violence occurred on several days of marching, with such rapid fluctuations of air-pressure that no heights could safely be deduced from the barometer-readings.

As regards the degree of reliability of the deduced levels, some little uncertainty exists in the levels adopted for the terminal points Siwa and El Fasher, while the temperature-compensation of the aneroid has not been tested and may not be quite perfect. Taking everything into account, it may be estimated that the levels of the principal camps are probably correct to within about twenty meters, while those of the intermediate camps and other points, for which only one or two readings of the barometer are available, may possibly be in error by twice that amount.

=7. Summary of Principal Geographical Positions and Levels=

_Latitude _Longitude _Meters _Remarks_
N._ E._ above
sea_

° ′ ″ ° ′ ″

Jaghbub (mosque) 29 44 41 24 31 11 32 Position from
previous
determination
by Dr. Ball.

Jalo (El Erg) 29 2 33 21 28 3 61

Bir Buttafal 28 54 26 21 45 15 98

El Harrash Well 25 26 29 22 10 55 310
(Zieghen)

Taj (Kufra) 24 13 47 23 23 41 475

Boema (Kufra. 24 13 8 23 24 40 400 Short compass
Rohlfs’s camp) traverse from
Taj

Arkenu 22 12 32 24 44 15 598

Ouenat 21 52 29 24 54 16 616

Erdi (camp 8 km. 18 35 39 23 10 29 906
north of well)

Agah 17 52 38 23 15 55 744

Enebah 17 21 24 23 14 28 1100

Bao 16 28 24 23 1 47 969

Furawia 15 21 51 23 38 10 857 Longitude
from Sudan map

=8. Construction of the Route Map on Scale 1:2,000,000=

In the process of utilizing the dead-reckoning for the determination of the longitudes of the principal camps, the whole route had been provisionally plotted on to a scale of 1:500,000 direct from the field-books, on a series of sheets each comprising one section of the route. To these plottings of the actual route were now added the computed levels of all camps, the geographical features fixed by cross-bearings on either side of the route, and notes on the nature of the ground. The various sections thus provisionally mapped on 1: 500,000 were then reduced to the scale of 1:2,000,000, allowance being made for the small departures of the original plottings from the 1:500,000 scale as found by the latitude-observations, and the various sections so reduced were drawn in on the final map between the finally adopted positions of the principal camps. It was found practicable to show all the principal geographical features on the final scale, though many notes on the nature of the ground had perforce to be omitted in order not to overcrowd the map. These notes are however carefully preserved on the 1:500,000 manuscript sectional maps in the Desert Survey Office in Cairo, so as to be available for future reference, while the principal of them are incorporated in Hassanein Bey’s narrative of the expedition.

The main portion of the route, namely that from Jaghbub to Furawia, has been mapped entirely from Hassanein Bey’s journals and note-books. The portions of his route from Sollum to Jaghbub in the north, and from Furawia to El Obeid in the south, have been copied from the latest official survey maps of Egypt and the Sudan, as being more accurate than any route survey could be.

The fixing of the positions of El Harrash and Taj by Hassanein Bey’s observations has enabled the course of his former expedition to Kufra (with Mrs. Forbes) in 1920-21 to be delineated more accurately than was possible from the original records of that journey, which were unaccompanied by any astronomical observations; and the course of the former route, adjusted to newly determined positions, has been indicated on the new map by a dotted line.

=9. Additions to Geographical Knowledge Resulting from the Expedition=

=Jalo.=—The first portion of Hassanein Bey’s route from Jaghbub to Jalo appears to be identical with that trodden by Rohlfs in 1869. At Gara Matan Sidi, about half-way between Jaghbub and Jalo, the track forks and Hassanein Bey went by the northern (Zawaiya) branch, which passes Hiseila Wells and enters Jalo from a more northerly direction than the southern (Majabra) branch taken by Rohlfs.

Hassanein Bey’s position for Jalo is almost identical with that of Rohlfs, but peculiar interest attaches to the former’s determination of its level at sixty-one meters above sea. Rohlfs, visiting the place in 1869 and 1879, had found the aneroid to indicate a level below the sea in 1869, and above it in 1879, and had ultimately concluded that both Aujila and Jalo lay about at sea-level.[4] Hassanein Bey’s determination is based on ten days’ aneroid readings and comparison with Siwa, and it is noteworthy that exactly the same altitude (sixty-one meters) for Jalo results whether the comparison is made with the readings of the standard barometer in the meteorological station at Siwa during the same period, or with the readings taken by Hassanein Bey with the same aneroid on four days at Siwa two months earlier (allowance being made, of course, for the annual variation of pressure over the intervening period). There can, I think, be hardly any doubt of the greater accuracy of Hassanein Bey’s determination, since it is unlikely that Rohlfs’s readings extended over so long a period, and it is practically certain that no comparisons were made by him with simultaneous observations at a place of known level. It should however be mentioned that Hassanein Bey’s level probably refers to a somewhat higher observation point than that of Rohlfs; for owing to sand-drifts enveloping the houses, the inhabitants of El Erg are gradually rebuilding their dwellings on higher ground, and his observations were taken in one of the most recently constructed of these. Another point worthy of remark is that although Hassanein Bey’s determination is to a certain extent checked by the exact agreement of the two methods of comparison above referred to, the day-to-day variations of pressure observed at Jalo are much in excess of those at Siwa during the same ten-day period. The extreme range shown by the aneroid at Jalo was 10 mm. against 5 mm. of the standard barometer at Siwa, and the 7 mm. average difference of pressure between the two places for the ten days of comparison, which has been used to calculate the new value of the level, is the mean of difference ranging from 1 to 12 mm. on different days. The relatively great variability of atmospheric pressure at Jalo, which readily explains the discordant results noted by Rohlfs on different dates, may be closely connected with the sand-storms which are so frequent in the neighborhood.

=Bir Buttafal.=—Bir Buttafal (“Battifal” of Rohlfs) is of importance as being the last watering-place for caravans proceeding on the weary desert march of nearly 400 km. to Zieghen. The position found for Bir Buttafal by Hassanein Bey agrees fairly well with that given by Rohlfs:[5]

_Meters
_Lat. N._ _Long. E._ above
sea_

° ′ ″ ° ′ ″

Bir Buttafal, Hassanein Bey 28 54 26 21 45 15 98

Bir Buttafal, Rohlfs 28 56 22 21 44 10 58
-------- -------- ----
Difference 1 56 1 5 40

=Zieghen= (“Sirhen” of Rohlfs).—Zieghen is the name of a district containing numerous wells. It is not inhabited, but is of great importance as lying on the main caravan route from Jalo to Kufra. The principal well used by the caravans is El Harrash. Rohlfs did not visit Zieghen; he traveled from Jalo to Kufra by the more westerly track through Taiserbo and Buseima, and the position shown for Zieghen on his map, which was based merely on his guides’ statements, is about 100 km. too far to the east-northeast.

As the journey from Jalo to Kufra by any future traveler is likely to be undertaken in the winter, when the question of fuel is second only to that of water, it is worth noting that the first _hatab_ (fire-wood) is met with at about 342 km. after leaving Bir Buttafal, and 52 before reaching El Harrash Well. In an emergency water may be got at Matan Abu Hosh, the old well of Zieghen, about 18 km. before reaching El Harrash; but El Harrash yields better water, and being the regular halting-place of the caravans, the water can usually be obtained there without digging; hence, unless the caravans are very thirsty they usually prefer to go on to El Harrash rather than make a halt at the old well. Excellent water can be got anywhere in the neighborhood of El Harrash by digging to a depth of three or four feet. From El Harrash to Buseima is about 54 km. in a direction a little west of south, and from El Harrash to Taj, the principal town of Kufra proper, is 182 km. in a southwesterly direction.

=Taiserbo.=—Taiserbo, the most northwesterly oasis of the Kufra group, has not, so far as is known, been visited by any traveler since Rohlfs’s day. Its position was however indicated to Hassanein Bey as lying between 70° and 80° west of north from El Harrash, at a distance of 60 to 70 km. This indication would place Taiserbo very nearly in the position which Rohlfs assigned to it. Rohlfs’s position for his camp at Kasr Djrangedi is probably therefore substantially correct, though it is likely that the oasis is in reality less extensive than shown on his map.

=Buseima.=—Although Buseima was not visited by Hassanein Bey on this occasion, his fixation of the position of El Harrash, in combination with his former rough compass-traverse from that place to Buseima with Mrs. Forbes in 1921, permits of a fair approximation for its position. Hassanein Bey’s estimates of distances and bearings on his former journey (adjusted by his recently observed latitudes at El Harrash and Taj) give his camp in Buseima as being 60 km. from El Harrash in a direction of 5° east of true south, and from his camp to that of Rohlfs (Ain El Nusrani) was roughly about 15 km. in a true west-northwesterly direction. Adopting Hassanein Bey’s recently fixed position for El Harrash, this would give a position for Rohlfs’s camp about 30 km. southwest by south of where Rohlfs placed it, as is shown by the following comparison:

_Lat. N._ _Long. E._

° ′ ″ ° ′ ″
Buseima (Rohlfs’s camp) from
Stecker’s observations 25 11 42 22 15 0

Buseima (Rohlfs’s camp) from
Hassanein Bey’s estimation 24 38 11 22 5 46
-------- --------
Difference 13 31 9 14

It would hardly seem possible that Hassanein Bey can have made so large an error as 25 km. in his former estimation of the distance of Buseima from El Harrash, and hence it would appear reasonable to think that there was some error either in Stecker’s observation or (what is more likely) in his reduction of it. This point is referred to further on in the discussion of the position of Boema (p. 334).

=Kufra= (Kebabo of Rohlfs).—The name “Kufra” is now generally applied, not to the whole of the Kufra group of oases as was done by Rohlfs in 1879, but specially to the area called Kebabo by that traveler.

The seat of local government and principal settlement is the walled town of Taj, situated on a rocky cliff overlooking the depression of the oasis proper which lies to the south and contains the villages of Jof, Buma, Boema, El Zurruk, Talalib, and Tollab. Hassanein Bey carried out latitude observations at Taj, and proceeded 3 km., on a bearing of 16° west of south, to Jof, from which place he made very careful estimations of the distances and bearings of the other villages of the oasis, which has enabled their relative positions to be plotted on the map with much closer approximation than had hitherto been possible.

Considerable interest attaches to the position of Boema, the easternmost village of Kufra, for it was here that Stecker camped with Rohlfs and made his observations for latitude and longitude in 1879. Hassanein Bey found Boema to lie 2 km. from Taj, in a direction 54° east of true south. Accepting his determination of the position of Taj, this leads to the following position for Boema as compared with that given by Rohlfs:

_Lat. N._ _Long. E._

° ′ ″ ° ′ ″

Boema, according to Hassanein Bey 24 13 8 23 24 40

“ “ Rohlfs[6] 24 31 38 23 12 40
-------- --------
Difference 18 30 12 0

Hassanein Bey thus places Boema some 40 km. south-southeast of the position assigned to it by Rohlfs from Stecker’s observations. The remarkable thing about this large discrepancy is that it is chiefly in the latitude, which was directly observed by Stecker at Boema itself, and by Hassanein Bey at Taj, only 2 km. away from Boema. I have not been able to find any details of Stecker’s observations, except that they were carried out with a “prismatic circle.” But I have subjected the original records of Hassanein Bey’s observations for time and latitude at Taj to very careful examination, and there is overwhelming evidence that his latitude for that place cannot be in error by more than 1′. He observed the altitude of Polaris at Taj on no fewer than six different nights, with a watch whose error on local time was accurately known from sun and star observations carried out on the same dates. From the internal evidence of the observations themselves, the watch-error at the time of sighting Polaris cannot on any occasion have been uncertain by more than two seconds, which would not, of course, sensibly affect the latitude found; the recorded magnetic bearing of the star sighted, as well as its rate of apparent motion, proves that the star used for latitude in each case was really Polaris; and the greatest difference of any single observed latitude from the mean of the six nights’ observations was only 15″, the average departure of a single observation from the mean being 12″. Hassanein Bey’s latitude of 24° 13′ 47″ for Taj can therefore be unhesitatingly accepted as correct within 1′; and since there is not room for an error of even this amount in his estimation of the short distance of Boema from Taj, it becomes absolutely certain that Rohlfs’s latitude for Boema is over a quarter of a degree too high.

It is curious to notice that in the case of Buseima (p. 332) the discrepancy of 13′ 31″ between Rohlfs’s latitude and that estimated from Hassanein Bey’s recent work is of the same order and of the same sign as that found at Boema; and that a negative correction equal in amount to the sun’s semidiameter would in each case bring the results of the two observers into fairly close agreement. The explanation hence suggests itself that Stecker may have determined his latitudes by observation of the upper limb of the sun at noon, and both at Buseima and Boema failed to correct the measured altitude for the semidiameter, thus making both latitudes 16′ too great. A mistake of this kind, as every scientific traveler knows, is very easily made in hurried reductions in the field; and at the time when Stecker carried out his observations and calculations in Kufra, both he and his brave leader were in imminent peril of losing their lives at the hands of treacherous Badawi.

A similar explanation may account to a large extent for the discrepancies of longitude at the two places. Thus, according to Hassanein Bey’s work, Rohlfs’s longitude for his camp at Buseima is 9′ too far east, and that for his camp at Boema 12′ too far west. We have only to assume that Stecker observed the sun’s lower limb in the morning at Buseima, and the upper limb in the afternoon at Boema, for finding the local times, and in each case omitted to correct the observed altitude for semidiameter, to account pretty completely for both discrepancies of longitude.

The puzzling thing about the above explanation of the errors of Rohlfs’s map is that Rohlfs actually traveled the distance between Buseima and Boema, and estimated it at 120 km.,[7] whereas Hassanein Bey’s positions would indicate that the true distance is 40 km. greater. But as Rohlfs’s statement of the distance was obviously written after Stecker had determined the positions of the places astronomically, it is probable that he obtained his 120 km. by calculation from the astronomical positions, rejecting any rough estimate he may have made of the distance from his times of marching. Both Hassanein Bey and Mrs. Forbes had considered that the true distance was much greater than 120 km. when they traversed it in 1921; but as on that occasion no observations for position were taken, it remained uncertain whether either Buseima or Boema had been wrongly placed on Rohlfs’s map. It is now practically certain that both were wrong.

As regards the level of Kufra, it is satisfactory to notice a very close agreement of Hassanein Bey’s observations with those of Rohlfs. Hassanein Bey’s barometer-readings at Ezeila, to the south of Jof, give 389 meters for the level of that place, and he estimates that Boema lies some ten meters higher; this would give about four hundred meters for the altitude of Boema, a figure identical with that found by Rohlfs. Taj, which has been built on the cliff north of Jof, since Rohlfs’s day, is found to be 475 meters above sea-level from a series of aneroid-readings extending over a fortnight. The outlying villages of Kufra which lie north of Taj are lower than Taj itself, but substantially higher than the southern villages of Kufra; Awadel is 434 meters above sea, and Hawari and Hawawiri are about the same altitude.

There is also fairly close agreement as to the extent of Kufra from north to south. Rohlfs’s map makes the extent in altitude between Hawawiri and Tollab to be about 35 km., while Hassanein Bey makes it 30 km. But when we come to the distance over which the villages extend from east to west, there is a much graver discrepancy. Rohlfs makes the extent from east to west (Buma to Tollab) about 40 km., while according to the latest estimations by Hassanein Bey the true extent is only about 21 km. As Rohlfs appears to have located many of the villages on his map merely from Arab statements, and not from careful personal estimation as did Hassanein Bey, we need have no hesitation in accepting the latter’s relative positions as by far the more nearly correct, and hence concluding that Rohlfs’s map gives an east and west extension which is nearly double the truth.

The error in east and west extension (so far as concerns the placing of the villages, not the extent of the vegetation) is even greater on the map prepared by me and published by Mrs. Forbes in 1921.[8] This is due to the distance between Jof and Tollab having been much overestimated on the former journey; it was given to me as about 42 km., while according to Hassanein Bey’s latest estimation it is only 20 km.

A matter which will at once strike the eye of any one who compares Hassanein Bey’s latest map of the Kufra villages with that published by Mrs. Forbes is that in the later map a place called Ezeila is shown south of Jof, while in the earlier map (which was prepared from Hassanein Bey’s own data and rough sketches) Ezeila is shown north of Hawawiri. The explanation is that there are _two_ Ezeilas. The name “Ezeila” is applied locally to any outlying well (usually with a clump of palms) which forms the last watering place for caravans leaving the oasis. Thus the northern Ezeila is the last well for a traveler leaving Kufra to go northeastward toward Jaghbub, while the southern Ezeila is the last well in Kufra for any one going south toward Wadai.

From the southern Ezeila of Kufra to Arkenu is 266 km. in a nearly southeasterly direction, and there is no water or grazing on the way. From Arkenu to Ouenat is a further 42 km. in a slightly more southerly direction.

=The Oases of Arkenu and Ouenat.=—One of the most interesting and important results of Hassanein Bey’s expedition is the confirmation of the real existence of the oases of Arkenu and Ouenat, and a fairly exact determination of their positions and altitudes. There has long been a tradition that two oases existed in or near the southwestern corner of Egypt. Thus the map of Africa on a scale of 1:4,000,000 published by Justus Perthes of Gotha in 1892 shows an unnamed small oasis and well in Lat. 21° 51′, Long. 23° 3′, and another “uninhabited oasis,” also unnamed, about 48 km. due east of it in Lat. 21° 50′, Long. 23° 29′. Both these oases were doubtless placed on the map from vague Arab statements; they appear not to have been previously visited by any explorer, and indeed their very existence was so doubtful that they have not been shown on the maps either of the English or of the French General Staff.

I have not been able to trace any published reference to the existence of Arkenu, but that of Ouenat has been mentioned in recent papers by Mr. Harding King and Lieutenant-Colonel Tilho. In Mr. Harding King’s paper of 1913[9] on “The Libyan Desert from Native Information,” he states that he heard of a place called “Owana” or “Owanat,” about half-way along a road from Merga to Kufra, where there is a well and green grass after rain. The map appended to his paper shows that Mr. Harding King’s estimate of its probable position was Lat. 21° 37′, Long. 24° 45′, which differs by nearly 130 km. from the nearer of the two oases shown on the above-mentioned German map.

Lieutenant-Colonel Tilho, who carried out exploratory work in Tibesti, Erdi, Borkou and Ennedi in 1912-17, mentions[10] “the still unknown massif of El Aouinat, situated approximately between the 22nd and 23rd degrees of latitude north and the 24th and 25th degrees of longitude east,” and a route he heard of from Aouinat to Merga.

Hassanein Bey’s observations give for the positions and altitude of his camps at Arkenu and Ouenat:

_Lat. N._ _Long. E._ _Meters
above sea_
° ′ ″ ° ′ ″

Arkenu 22 12 32 24 44 15 598

Ouenat 21 52 29 24 54 16 616

Thus Ouenat is only some 34 km. from where Mr. Harding King guessed its position to be from his guide’s statements, but it is outside the somewhat wide limits of latitude indicated by Lieutenant-Colonel Tilho, and is nearly 150 km. from the place marked “uninhabited oasis” on the German map; while Arkenu, which is presumably the small oasis marked to the west of the “uninhabited oasis,” is now proved to be some 180 km. from where it is shown on that map.

It may be remarked that Arkenu is well within the boundaries of Egypt, while Ouenat is a short distance over the boundary, in the Anglo-Egyptian Sudan.

The principal interest in these places lies in the possibilities they open up for further exploration of the southwest corner of Egypt, which has hitherto been inaccessible to military patrols, and even to the boldest of explorers, by reason of the absence of any certain knowledge as to the existence and position of permanent water-supplies. Now that Arkenu and Ouenat are exactly located, with the existence of drinkable water in reasonable quantities, it may be possible for a traveler from Egypt to reach them and procure the necessary water-supplies for his return journey. I say it _may_ be possible, for there are still great difficulties about access to Arkenu and Ouenat from Egypt, although both the compilers of the German map and Mr. Harding King were informed that an old track to Egypt runs from Ouenat. According to Mr. Harding King’s informant, the track runs to Dakhla Oasis, which is a distance of some 600 km. through a waterless desert, and consequently the journey between the two places is a very formidable undertaking for camels, even in winter; while the suitability of the ground for motor-cars, especially in the mountainous region round the oases themselves, is as yet unknown.

An interesting feature of Arkenu and Ouenat is that they are not depressions with underground water-supplies, like all the other oases of the Western Desert of Egypt, but mountainous areas where the water is dependent on local rainfall and collected in natural basins in the rocks.[11] The Nile Valley in the same latitudes has practically no rainfall, but here, some 700 km. westward into the Sahara, there is sufficient rain to maintain perennial though limited supplies—at Ouenat even sufficient for the needs of a settlement of some one hundred and fifty Badawi—and at certain seasons to provide grazing for animals in the valleys and lowlands. The ground-level in this region is high (six hundred meters above sea-level), but the mountains near the oases rise to heights of over eleven hundred meters above the sea, and it can hardly be doubted that the rainfall is connected with the orography, the mountains attracting or helping to form clouds. In this connection it is worth noting that in the more open country further south, as well as in that to the north, the absence of vegetation shows that rainfall is evidently much scarcer than in the mountains around the oases; also that Ouenat, where the mountains are higher than at Arkenu, possesses better and more abundant water. The conservation of the water through the dry season is partly conditioned by the almost impermeable nature of the crystalline rocks composing the mountains, and partly by the sheltered position of the pools in the rocky gullies, which diminishes evaporation.

The full extent of the mountains of Arkenu and Ouenat is not yet known, but they cover at least 1000 square km. Hassanein Bey’s main route lay along the western feet of the masses, so that their western limit is ascertained, as also their north and south extension; but their eastern limits in Egypt are unknown, and it is not yet certain whether there may be a continuous chain of hills connecting the two masses to the east. Hassanein Bey made a round reconnaissance extending some 40 km. eastward of his camp at Ouenat, without reaching the limits of the mass. The mountains are visible from great distances from the north and south, Arkenu having been sighted from at least 60 km. north, and Ouenat remained visible for at least the same distance on the track southward from it. There is a possibility that the mountains may be less conspicuous to a traveler approaching from the east, owing to their breaking up into smaller hills and the ground on that side of them being higher and falling away gradually toward the Nile; but this must remain uncertain until further exploration is undertaken.

From Ouenat to Erdi “Well” is a journey of 439 km. in a south-southwesterly direction, the first 284 km. being in the Anglo-Egyptian Sudan, the remaining 146 in French Equatorial Africa. There is no water in all this stretch, but patches of dried grass were met with at intervals in the latter half of the journey, and some 25 km. before reaching Erdi the valleys were full of green grass. Thus the northern limit of the equatorial rain-belt hereabouts is approximately in Lat. 18° 50′.

=Erdi.=—Erdi appears to be the name given to an extensive tract of country stretching between the twenty-first and twenty-fourth meridians of east longitude, rising gradually southward and ending in a broken east and west escarpment in about Lat. 18° 30′. The water-source visited by Hassanein Bey, called by the guide “Erdi Well,” is in Lat. 18° 31′, Long. 23° 10′, and is 958 meters above sea-level. It is not really a well, but a rock-pool, similar to those of Arkenu and Ouenat; the water is good.

Hassanein Bey’s “Erdi Well” is close to the locality marked “Erdi-ma” on Lieutenant-Colonel Tilho’s map of 1920, but it appears not to be the same water-source as the one visited by that traveler. Erdi Well is at the head of a small valley draining northward, and one has to ascend the hills to a height of 1020 meters above sea and cross a stretch of broken plateau before reaching the southward drainages which cut back into the scarp. Over this broken plateau Hassanein Bey proceeded in a southeasterly direction, descending the scarp in Lat. 18° 25′, Long. 23° 20′. The level at the foot of the scarp was 790 meters, so that the scarp hereabouts is some 230 meters in height.

After descending the Erdi scarp, Hassanein Bey’s track southward across the great sandy depression which separates the Erdi plateau from that of Ennedi, to Agah (88 km. from his camp north of Erdi Well), appears to have been almost parallel to, and some 20 km. east of, that followed by Lieutenant-Colonel Tilho in 1914.

=Agah.=—The water-source of Agah is a rock-pool similar to that at Erdi; but the water is bad, owing to fouling by animals. The pool is some 6 km. up a valley cutting back northward into the scarp which faces that of Erdi. The position found for the pool at Agah lies some 24 km. from the “Aga Spring” shown on Lieutenant-Colonel Tilho’s map. There are possibly several springs and pools among the hills in this neighborhood, all bearing the same name, which would explain the apparent discrepancy.

From Agah the track to Enebah (65 km.) runs in a rather zigzag course with a general southward trend. For the first 10 km. beyond the pool, the track ascends the valley; then, mounting rapidly, it soon reaches altitudes of over a thousand meters on the plateau.

=Enebah.=—Here is a small settlement of Badawi and a well of good water about 28 km. east of the wells of Keita shown on Lieutenant-Colonel Tilho’s map, on the same high plateau.

From Enebah to Bao is 120 km., by a rather zigzag track in a general south-southwesterly direction over an undulating and hilly plateau. The greatest altitude recorded by Hassanein Bey during his entire journey, 1184 meters above sea, was reached at a point on the road about 18 km. from Enebah. This altitude (3884 feet) is slightly higher than that (3600 feet) which Lieutenant-Colonel Tilho records as his maximum on the same (Erdebe) plateau at a point further west; so that the plateau probably increases in height to the eastward. The Kaptarko valley was crossed about 47 km. further on, and it is interesting to note that Hassanein Bey’s data give a position for this which is very close to the “Kapterko” of Lieutenant-Colonel Tilho’s map.

=Bao.=—Hassanein Bey’s Bao is not the “Bo” visited by Lieutenant-Colonel Tilho, which lies over 100 km. further north, but the place called “Orobo” on Tilho’s map and “Bao” on the map of Wadai and Darfur which was attached to the convention between the British and French Governments at Paris in 1919; this is evident from the following comparison of Hassanein Bey’s position with those scaled for the above-mentioned places from the maps referred to:

_Lat. N._ _Long. E._

° ′ ″ ° ′ ″

Bao (Hassanein Bey) 16 28 24 23 1 47

Orobo (Tilho) 16 30 0 22 59 0

Bao (convention map) 16 28 0 23 4 0

The wells of Bao are at the head of a small valley draining northward, in which shrubs and trees are plentiful. There are several wells, with perennial supplies, though the water becomes scarce in the dry season and the wells have then to be deepened.

From Bao to Furawia is 145 km. in a south-southeasterly direction, over ground partly covered with grass and small trees. About 55 km. before reaching Furawia, Hassanein Bey passed close to a hill called Tameira, on which is a sign-post, formed of a dead tree, marking the boundary between French and Anglo-Egyptian territory. No astronomical observations were taken here, but Hassanein Bey’s adjusted traverse-data indicate the approximate position of the hill to be Lat. 15° 48′ N., Long. 23° 27′ E. The Wadai Hawar (“Howa” of the Anglo-French convention map) was crossed about 7 km. beyond Tameira Hill.

=Conclusion.=—In concluding this analysis of Hassanein Bey’s results, the reduction of which has occupied a large part of my time for over two months, I may be permitted to remark that his expedition appears to me to be an almost unique achievement in the annals of geographical exploration. The journey of 3345 km. from Sollum to El Obeid, most of it through inhospitable deserts sparsely inhabited by fanatical and predatory tribes, is one which, without a strong military escort, could have been undertaken only by a Moslem, and by one of remarkable grit, tact, and perseverance. But Hassanein Bey has not only accomplished this difficult journey and brought back interesting descriptions and photographs of the country through which he passed. Before setting out from Cairo he had applied himself strenuously for several weeks to acquiring facility in the use of the theodolite, and instruction in the particular methods of reconnaissance-survey best adapted for exploration of the kind on which he was to embark; and throughout his travels he made excellent use of the surveying knowledge thus acquired. How complete and accurate were his observations will be obvious from the foregoing analysis; and the really remarkable thing is that he managed somehow to carry out all this observation single-handed, and to maintain the continuity and accuracy of his measurements and records over the distance of more than 2000 km. which separates the points on his route whose positions were previously known. Thanks to the detailed and systematic character of his observations, their reduction has been a pleasant labor, and it has been comparatively easy to map his route and the newly discovered places along it with a high degree of accuracy.

The principal additions to our knowledge of northeastern Africa which have resulted from the expedition are:

(1) The true positions of Zieghen and Kufra, resulting in changes of about 100 and 40 kms. respectively from the positions hitherto assigned to these places on maps of Africa.

(2) The discovery of the oases of Arkenu and Ouenat, previously unknown, and the determination of their positions and approximate extent, thus opening up possibilities of new desert travel from Egypt into regions of the Libyan Desert still unexplored.

(3) The discovery of a route from southwestern Egypt across the Erdi and Ennedi plateaux of French Equatorial Africa into Darfur, and the positions of the water-sources along it. Incidentally, this establishes a connection with, and extension of, Lieutenant-Colonel Tilho’s recent brilliant explorations in the French Sudan.

(4) The determination of careful barometric levels along the entire route, affording valuable information on the orography of a vast region of which little was previously known, and confirming Lieutenant-Colonel Tilho’s conclusion that there is no possible drainage-outlet from Lake Chad in an easterly direction.

[Footnote 1: Since the above was written, I have received information from the director of Sudan surveys that a recent extension of the Sudan triangulation-net includes Gebel Furawia as one of the points, and that the precise position found for the summit of the hill is Lat. 15° 20′ 59.9″ N., Long. 23° 36′ 48.1″ E., altitude 954 meters above sea-level. This position differs by about 2 km. from that shown on the map above referred to; but in view of the fact that the distance and bearing of Hassanein Bey’s camp from the hill is unknown, though his observed latitude shows his camp to have been on a parallel about a kilometer and a half north of the hill, I have not thought it worth while to make any change in the adjustment of Hassanein Bey’s data. The longitude adopted for the camp (p. 320) may be slightly in error, but it is unlikely that the error can exceed a mile or so. The difference of level between the top of the hill and Hassanein Bey’s camp being unknown, the triangulation-level affords no control over Hassanein Bey’s barometric value for the latter place, and consequently I have judged it best to use El Fasher as the south control point in adjusting the level-determinations.]

[Footnote 2: No observations are known to have been taken at Jedabia. The position given is that which I adopted for it in preparing a former map in 1921, and was arrived at by estimation from a car-and-compass traverse carried out by Captain Williams from Zuetina in 1918.]

[Footnote 3: See foot-note, p. 316.]

[Footnote 4: Rohlfs, “Kufra,” 1881, p. 226.]

[Footnote 5: “Mitt. Afrik. Ges.,” Band ii., 1880-81, p. 17.]

[Footnote 6: “Mitt. Afrik. Ges.,” Band ii., 1880-81, p. 25.]

[Footnote 7: “Mitt. Afrik. Ges.,” Band ii., 1880-81, p. 23.]

[Footnote 8: “Geographical Journal,” Vol. 68 (1921), p. 248.]

[Footnote 9: “Geographical Journal,” Vol. 42 (1913), p. 282.]

[Footnote 10: “Geographical Journal,” Vol. 46 (1920), p. 98.]

[Footnote 11: Though rare in the Western Desert of Egypt, these rock-basins are common in the mountains of the Eastern Desert near the Red Sea, where they are called _galts_. See my “Geography and Geology of South-Eastern Egypt” (1912), p. 240. They are also abundant in the Erdi and Ennedi regions of French Equatorial Africa, as we know from the explorations of both Lieutenant-Colonel Tilho and Hassanein Bey.]