Chapter XXIII: Letter XIX: gives a definition of the ellipsis, which would be a (17)

We may also consider this problem in another point of view, with which it is convenient to make ourselves familiar. The duration of each undulation, as we have seen, does not depend on the greater or less velocity with which the [p446] agitation is propagated along the fluid, but merely on the duration of the previous oscillation which gave it birth; consequently, when the luminous waves pass from one medium into another, in which they are propagated more slowly, each undulation is performed in the same interval of time as before, and the greater density of the medium has no other effect than that of diminishing the length of the undulation, in the same proportion as the velocity of light is diminished: for the length of the undulation is equal to the space that the first agitation describes during the time of a complete oscillation. We may therefore calculate the relative velocities of light in different mediums, by comparing the length of the undulations of the same kind of light in those mediums. Now, the middle of the central stripe is formed by the reunion of such rays of the two pencils as have performed the same number of undulations, in their way from the luminous point, whatever may be the nature of the mediums transmitting the light. If then the central stripe is brought towards the side of the pencil which has passed through the glass, it is because the undulations of light are shorter within the glass than in the air; and it is necessary, in consequence, that the path described on this side should be shorter than the other, in order that the number of undulations may remain the same. Let us suppose, then, that the central stripe has been displaced to the extent of twenty breadths of fringes, for example, or of twenty times the interval between the middle points of two consecutive dark stripes; we must necessarily conclude that the interposition of the plate of glass has retarded the progress of the pencil passing through it to the extent of twenty undulations; or that it has performed within the plate twenty undulations more than the same pencil would have performed in an equal thickness of air, since each breadth of a fringe answers to the difference of a single undulation. If then we know the thickness of the plate, and the length of an undulation of the light employed, which is easily deduced from the measurement of the fringes, by the formula that has been given, we can calculate the number of undulations comprehended in the same thickness of air, and by adding twenty to the number, we shall have that of the [p447] undulations performed in the thickness of the glass; and the proportion of these two numbers will be that of the velocities of light in the different mediums. Now this proportion is found by experiment the same with that of the sines of incidence and of refraction between air and glass; which agrees with the theory of the refraction of undulations, as will be seen hereafter.

The same experiment may be employed, on the other hand, for determining with extreme precision the thickness of a thin plate of a substance of known refractive density; placing it in the way of one of the two pencils of light, and measuring the displacement of the fringes which it occasions.

This method of determining refractive densities is however liable to some difficulties, when we wish to apply it to a body much more dense than air, such as water, or glass, for example; since it is necessary to employ a very thin plate only, in order that the fringes may not be too much displaced for observation; and then it becomes difficult to measure the thickness of such a plate with sufficient accuracy. We may, indeed, place in the way of the other pencil a thick plate of a transparent substance, of which the refractive density has been ascertained by the ordinary methods, and we can then employ as thick a plate of the new substance. But then it becomes simpler to measure its refractive density by the common method: [unless we choose to immerse the whole apparatus in a fluid very nearly approaching to it in refractive density, which may sometimes be done without inconvenience. TR.]

The case, in which Mr. Arago’s experiment has a decided advantage over the direct method, is when we desire to determine very slight differences of velocity in mediums of nearly equal refractive density: for by lengthening the passage of the light in the two mediums of which we wish to compare the refractive density, we can increase the accuracy of the results almost without limit. In order to form an idea of the extreme precision that may be attained by these measurements, it is sufficient to observe that the length of the yellow undulations in air being about .000021 E.I., there are two millions of them in the length of about 42 inches. Now [p448] it is very easy to observe the difference of one fifth of a fringe, which corresponds to a retardation of one fifth of an undulation in one of the pencils, that is, the ten millionth part of the whole length of 42 inches; we might therefore, by introducing any gas or vapour into a tube of this length, terminated by two plane glasses, estimate very accurately the variation of its refractive power.

I take the length of an undulation of the yellow rays, which are the most brilliant of the spectrum, and of which the dark and light stripes consequently coincide with the darkest and brightest stripes of the fringes produced by white light, which is commonly employed in these experiments, both because of its greater brightness, and because of the more marked character which it gives to the central stripe, so as to prevent any other from being mistaken for it.

It was an apparatus of this kind that Mr. ARAGO and myself employed for measuring the difference of the refractive powers of dry air, and of air saturated with moisture at 80° F., which is so small, that it would escape every other method of observation, because the greater refractive power of aqueous vapour is almost exactly compensated by the less specific gravity of moist air. But, in the generality of cases, the slightest mixture of one vapour or gas with another produces a considerable displacement in the fringes: and if we had a series of experiments of this kind, made with care, the apparatus might become a valuable instrument of chemical analysis.

[To be continued.]

iii. _Remarks on the Action of_ CORPUSCULAR FORCES. _In a Letter to_ Mr. POISSON.

My dear Sir,

I am very glad to see that you have been applying your analytical powers to the investigation of the acustical effects of corpuscular forces, and that, among many more refined determinations, you, have confirmed several of the results relating to sounding bodies, which were published twenty years ago in my Lectures on Natural Philosophy: though they were generally such as might have been derived from the calculations of Bernoulli and Euler; which I attempted in some [p449] measure to simplify by the introduction of the element which I called the _Modulus of Elasticity_ of each substance. You have very properly observed that it is often difficult to represent the combination of these corpuscular forces by an integral, since in many practical cases the integral must vanish, where it would naturally be applied to the phenomena: and, from similar considerations, I trust you will be prepared to admit the objections that I made long ago, to the reasoning of your great predecessor, Mr. Laplace, to whose station in the mathematical world you appear so eminently qualified to succeed.

The equation, which may be called final, in Mr. Laplace’s Supplement to the Xth Book, p. 47, is _Q_ cos. (ω−θ) = (2ς−ς′) _K_ sin. θ. Now this, in my opinion, is a perfect _reductio ad absurdum_: for _Q_ must _always_ be _incomparably_ less than _K_; the attraction of the particles lying between a cylinder and its tangent plane being _always_ infinitely less than that of the particles in an angular or prismatic edge: or if this were denied in general, it would obviously become true when the cylinder itself becomes a plane, and _Q_ vanishes altogether; which will always be the state of the problem, when the surface of the solid is so inclined to the horizon, that the surface of the fluid may remain horizontal, the appropriate angle of contact being unaltered in these circumstances, as it is easy to show by making the experiment with mercury.

I entreat you to consider this objection with patient attention, and to tell me if you can find any arguments to supersede it. I would also presume to ask your opinion of my own method of deducing the force of capillarity from the elementary attractions and repulsions of bodies, at the end of my Illustrations of the Celestial Mechanics, Art. 382; Appendix A, p. 329 to 337. The volume is in the Library of the Academy; or I should have taken the liberty of sending you a copy, as an inadequate return for so many valuable communications with which you have had the kindness to favour me.

Believe me always, dear Sir, Very truly yours, * * * *

_London_, 18 _Nov._ 1827.

[p450]

iv. _Calculations of_ LUNAR PHENOMENA. _By_ THOMAS HENDERSON, Esq.

----------------------------------------------------------------------+
Principal LUNAR OCCULTATIONS of the Fixed Stars in the |
Months of January, February, March, and April, 1828; calculated |
for the Royal Observatory at Greenwich. |
---------+---------------+------+--------------+-------------+--------+
| | | Immersion and| Apparent |Point of|
Date. | Names of |Magni-| Emersion. |Difference of| Moon’s |
| Stars. |tude. | Mean Time. |Declination. | Limb. |
---------+---------------+------+--------------+-------------+--------+
| | | H. M. S. | ′ * ″ | ° |
Jan. 4|κ Cancri | 5.6 |Imm. 10 51 43 | 13 18 S. | 172 R. |
| | |Em. 11 44 48 | 7 19 S. | 91 R. |
31|α^1 Cancri | 6 |Imm. 11 14 52 | 7 45 S. | 134 L. |
| | |Em. 12 35 56 | 2 19 N. | 88 R. |
" |κ Cancri | 5.6 |Imm. 18 38 0 | 0 58 N. | 47 L. |
| | |Em. Under | Horizon. | |
Feb. 7|α^2 Libræ | 3 |Imm. 20 29 54 | 1 35 S. | 69 L. |
| | |Em. 21 37 54 | 4 33 N. | 107 R. |
22|δ^3 Tauri | 5 |Imm. 7 0 9 | 3 47 S. | 90 L. |
| | |Em. 8 16 39 | 6 34 S. | 146 R. |
28|ω Leonis | 6.7 |Imm. 11 24 25 | 14 57 S. | 165 L. |
| | |Em. 12 3 15 | 9 17 S. | 145 R. |
March 10|ρ^1 Sagittarii | 5 |Imm. 16 14 54 | 4 24 N. | 105 L. |
| | |Em. 17 20 39 | 1 25 N. | 62 R. |
23|u Geminorum | 5.6 |Imm. 8 4 36 | 2 48 N. | 55 L. |
| | |Em. 9 18 11 | 7 46 N. | 94 R. |
24|k Geminorum | 5 |Imm. 9 12 5 | 3 53 S. | 78 L. |
| | |Em. 10 28 34 | 3 55 N. | 111 R. |
26|κ Cancri | 5.6 |Imm. 7 41 25 | 7 6 S. | 132 L. |
| | |Em. 9 3 38 | 3 14 N. | 83 R. |
April 2|ν^1 Libræ | 6 |Imm. 14 7 43 | 12 43 N. | 38 L. |
| | |Em. 14 34 56 | 15 49 N. | 10 R. |
|ν^2 Libræ | 6.7 |Imm. 13 58 36 | 2 1 S. | 99 L. |
| | |Em. 15 13 58 | 6 19 N. | 76 R. |
29|α^1 Libræ | 6 |Imm. 16 15 38 | 14 48 S. | 126 L. |
| | |Em. 16 48 16 | 11 55 S. | 174 R. |
|α^2 Libræ | 3 |Imm. 16 33 5 | 15 54 S. | 145 L. |
| | |Em. 16 43 5 | 15 3 S. | 162 L. |
---------+---------------+------+--------------+-------------+--------+
The fifth column shows the apparent difference of declination
between the Star and Moon’s centre at the immersion and emersion;
the letters N and S denoting the Star to be north or south from the
Moon. The sixth or last column shows the point of the Moon’s limb
where the immersion and emersion take place, reckoning from the
vertex or highest point; the letters L and R signifying to the left
hand or right hand of the observer.

An error of 11 seconds in the computed difference of declination between the Moon and Star, will be sufficient to convert the expected Occultation of α^2 Libræ, on 29th April, into an Appulse; and a less error will considerably affect the times and places of immersion and emersion. [To be continued.] +----------------------------------------------------------------------+

[p451]

+----------------------------------------------------------------------+ ELEMENTS for computing the ECLIPSES of the SUN and OCCULTATIONS of the PLANETS by the Moon, in the Year 1828.

Conjunction in Diff. Relat Relative ☉ or Pla ☉ or Pla A. R. Apparent Dec. ive Orb. Ang. net’s A. net’s N. Time. H. M. R. at ☌ P. D. at ☌ ☽ D. H. M. S. ′☽ ″ ′ ″ ° ′ H. M. S. ° ′ ″ ♃ Jan. 11 10 47 11 21 1 S. 34 6 S. 76 58 E. 14 35 47 104 2 30 ♂ Jan. 11 16 40 36 4 29 N. 33 14 S. 78 4 14 49 29 105 12 34 ♃ Feb. 7 22 17 54 5 44 N. 33 26 S. 77 35 14 46 40 104 48 7 ♃ Mar. 6 4 48 7 16 46 N. 33 29 S. 77 47 14 49 7 104 53 57 ♃ April 2 8 6 49 9 6 N. 34 12 S. 77 26 14 42 44 104 21 7 ☉ April 13 21 23 53 8 50 N. 31 23 N. 74 7 1 30 20 80 32 14 ♃ April 29 10 49 53 9 3 S. 34 50 S. 76 40 14 30 21 103 22 5 ☿ May 12 8 58 41 7 44 N. 27 31 N. 78 28 2 30 50 76 35 6 ♃ May 26 14 58 46 20 58 S. 34 38 S. 75 54 14 17 53 102 23 57 ♃ June 22 21 27 33 14 27 S. 33 40 S. 75 26 14 11 5 101 55 51 ♀ July 13 12 0 30 68 43 S. 30 15 S. 76 50 8 55 0 76 17 27 ♃ July 20 6 18 33 10 12 N. 32 33 S. 75 28 14 12 35 102 11 28 ♃ Aug. 16 17 18 6 44 49 N. 31 50 S. 75 59 14 22 10 103 7 21 ♀ Sept. 5 3 7 12 4 10 S. 28 8 S. 78 3 8 13 4 75 7 21 ☉ Oct. 8 12 23 35 6 39 S. 29 6 S. 73 2 12 57 44 96 10 27 ♀ Dec. 3 13 30 46 39 10 S. 29 39 S. 75 23 14 3 58 100 19 38

Conjunction in A. Nearest Time of { ☉ or Planet’s } R. Apparent Time. Approach. nearest Horary Motion Semi- Hor. Approach, in A. in N. diam- Par. Apparent R. in P. D. eter Time. Time. ☽ D. H. M. S. ′ ″ D. H. M. S. SEC. ″ ″ ″ ♃ Jan. 11 10 47 11 20 28 11 10 38 51 + 1·3 + 6 17 2 ♂ Jan. 11 16 40 36 4 23 11 16 42 16 + 5·9 + 27 3 5 ♃ Feb. 7 22 17 54 5 36 7 22 20 7 + 0·6 + 2 18 2 ♃ Mar. 6 4 48 7 16 23 6 4 54 29 − 0·2 − 1 20 2 ♃ April 2 8 6 49 8 53 2 8 10 18 − 0·9 − 4 21 2 ☉ April 13 21 23 53 8 30 13 21 19 16 + 9·2 − 54 958 9 ♃ April 29 10 49 53 8 48 29 10 46 17 − 1·2 − 6 22 2 ☿ May 12 8 58 41 7 35 12 8 55 19 +19·8 −119 3 7 ♃ May 26 14 58 46 20 20 26 14 49 55 − 0·9 − 4 21 2 ♃ June 22 21 27 33 13 59 22 21 21 5 − 0·3 − 1 20 2 ♀ July 13 12 0 30 66 55 13 11 29 28 − 3·4 + 22 26 27 ♃ July 20 6 18 33 9 53 20 6 23 16 + 0·5 + 3 18 2 ♃ Aug. 16 17 18 6 43 29 16 17 38 31 + 1·2 + 6 17 2 ♀ Sept. 5 3 7 12 4 5 5 3 5 22 + 5·8 − 1 18 19 ☉ Oct. 8 12 23 35 6 21 8 12 19 35 + 9·2 + 57 963 9 ♀ Dec. 3 13 30 46 37 54 3 13 10 46 +11·5 + 61 7 8

The places of the Sun and Moon have been taken from the Nautical Almanac, those of Mercury from Lindenau’s Tables, and those of the other Planets from Schumacher’s Ephemeris.——The sign + denotes the motion in A. R. to be direct; the sign −, retrograde. The sign + denotes the motion in N. P. D. to be towards the South; the sign − towards the North.——None of the preceding Conjunctions will prove to be an Eclipse or Occultation visible at Greenwich. +----------------------------------------------------------------------+

[p452]

+-----------------------------------------+ Apparent Distance of Jupiter’s Satellites from Jupiter’s Centre, at his Conjunctions in A. R. with the Moon.

+------------+----------+-----------------+
Date. Satellite. Distance.
+------------+----------+-----------------+
1828. ′ ″
+------------+----------+-----------------+
January 11 I. 1 14 East
II. 0 51 ----
III. 4 16 West
IV. 2 21 ----
February 7 I. 1 6 West
II. 2 40 East
III. 2 16 West
IV. 4 27 ----
March 6 I. 1 51 East
II. 2 24 West
III. 3 14 East
IV. 8 44 ----
April 2 I. 1 44 West
II. 0 15 ----[A]
III. 4 58 East
IV. 7 30 West
29 I. 0 14 West[B]
II. 2 51 East
III. 0 32 West
IV. 1 6 East
May 26 I. 1 44 East
II. 3 8 West
III. 5 15 ----
IV. 6 38 East
June 22 I. 1 59 West
II. 0 4 East[C]
III. 3 10 West
IV. 8 56 ----
July 20 I. 1 51 East
II. 2 50 ----
III. 1 55 ----
IV. 4 51 ----
August 16 I. 1 43 West
II. 1 12 ----
III. 4 21 East
IV. 1 53 ----
+------------+----------+-----------------+
A: On Jupiter’s disk. B: Eclipsed.

C: On Jupiters disk.

These Configurations have been computed
from De Lambre’s Tables.
+-----------------------------------------+

[p453]

MISCELLANEOUS INTELLIGENCE.

I. MECHANICAL SCIENCE.

1. _On the Adhesion of Screws_.—The following results, respecting the force necessary to draw iron screws out of given depths of wood, are by Mr. Bevan, and should be placed by the side of those he has given with regard to nails[128].

“The screws I used were about two inches in length, 0.22 diameter at the exterior of the threads, 0.15 diameter at the bottom, the depth of the worm or thread being 0.035, and the number of threads in one inch = 12. They were passed through pieces of wood exactly half an inch in thickness, and drawn out by the weights specified in the following table:

Dry beech 460 pounds Do. Do. 790 Dry sound ash 790 Dry oak 760 Dry mahogany 770 Dry elm 655 Dry sycamore 830

“The weights were supported about two minutes before the screws were extracted.

“I have also found the force required to draw similar screws out of deal and the softer woods about half the above.

“From which we may infer as a rule to estimate the _full_ force of adhesion, in hard wood . . . 200.000 _d_ δ _t_ = _f_, and in soft wood . . . 100.000 _d_ δ _t_ = _f_, _d_ being the diameter of the screw; δ the depth of the worm or thread; and _t_ the thickness of the wood into which it is forced;—all in inches; _f_ being the force in pounds to extract the same.” We may, from the above experiments, observe the approximation to perfection in the art of screw making; for had the screw been greater in diameter, there would have been a waste of material, or had it been less, it would not have been sufficiently strong, which may be proved as follows: the cohesion of wrought iron has been found, from a number of experiments, to be about 43000 lbs. per cylindrical inch; and as the smallest diameter of screw used in my experiment was 0.15, it would have been torn asunder by a force of about 968 lbs.; or if the hard wood had been about 5/8 of an inch thick into which it had been screwed, the screw would have been broken instead of forcing its passage out of the wood.—_Phil. Mag. N. S._ ii. 291.

FOOTNOTE:

[128] See page 360, vol. xvii. of the former series of this Journal.

2. _Improvement in Steam-engines_.—According to the valuable records kept of the duty of the steam-engines at the mines in Cornwall, a most important improvement has been effected in two [p454] instances, of engines erected by Captain Samuel Grose; dependent entirely upon attention to the smaller details of the machines. The best engines, heretofore, had not done more than raise forty millions of pounds of water one foot high, by each bushel of coals consumed, except indeed upon short occasions. In one of the cases in question, an engine at Wheal Hope, of sixty-inch cylinder, working single as usual, the duty rose to fifty, fifty-four, and fifty-five millions of pounds; and in the other, an engine of eighty-inch cylinder, at Wheal Towan, the duty rose in

April 61,877,545 May 60,632,179 June 61,762,210 July 62,220,820 August 61,764,166

thus exceeding by nearly fifty per cent. what had been effected before that time.

3. _Improved Clock_.—Among the articles displayed at the first National Exhibition of the Objects of Arts and Industry, at Neufchatel, Switzerland, last year, was a clock made by F. Houriet, of Locle; in which steel was used only in the main springs and in the axes of the moveable parts; all the other parts were in brass, gold alloy, and white gold. The number of pieces in gold, gold and silver, gold and platina, is sixty-two: all the pivots turn on jewels, and the functions of the free escapements are effected also by means of pallets in precious stones. It had been supposed that the escapements and the spiral spring not being of steel, inconvenience would result from the smaller degree of elasticity, but numerous trials with favourable results have removed the objection; and it appears that gold, hardened either by hammering or other means, is more elastic than hardened and untempered steel. The clock had gone for six days, exposed to the contact of a magnet competent to lift twenty-five or thirty pounds, without suffering any derangement.—_Rév. Ency._

4. _Method of dividing Glass by Friction_.—The following method is described by Dr. Hare: “Some years ago Mr. Lukin showed me that a small phial or tube might be separated into two parts, if subjected to cold water after being heated by the friction of a cord made to circulate about it, by two persons alternately pulling in opposite directions. I was subsequently enabled to employ this process in dividing large vessels of four or five inches in diameter, and likewise to render it in every case more easy and certain by means of a piece of plank forked like a boot-jack, and also having a kerf cut by a saw, parallel to and nearly equidistant from the principal surfaces of the plank, and at right angles to the incisions productive of the fork.

“By means of the fork, the glass is easily held steadily by the hand of one operator; by means of the kerf, the string, while [p455] circulating about the glass, is confined to the part where the separation is desired. As soon as the cord smokes, the glass is plunged in water, or if too large to be easily immersed, the water must be thrown upon it; the latter method is always preferable when, upon immersing the body, the water can reach the inner surface. As plunging is the most effectual method of employing the water in the case of a tube, I usually close the end which is to be immersed.”—_Silliman’s Journal_, xiii. 7.

5. _Use of Soapstone in diminishing Friction_.—In a letter to Professor Silliman upon this subject, Mr. E. Bailey of Boston, says, “I understand the Soapstone has been used for this purpose in the extensive manufactories at Lowell, for about two years, and with great profit and success. Besides answering the purpose to which it is applied very much better than any other substance that can be procured, it saves a great deal of trouble and expense. It is first thoroughly pulverized, and then mixed with oil, tallow, lard, or tar, whichever may be the best adapted to the use for which it is designed. It is of course important to procure that which is free from _grit_, and it can be purified in a good degree by mixing the powder with oil, and decanting it after it has stood a few minutes. The heavier particles will form a sediment to be rejected. It is used in all kinds of machinery where it is necessary to apply any unctuous substance to diminish friction, and it is said to be an excellent substitute for the usual composition applied to carriage-wheels.”

Some idea of the value of soapstone thus applied, may be formed from the following fact communicated by D. Moody, Esq., the superintendent of the tar-works on the mill-dam near this city. Connected with the rolling machine of that establishment, there is a horizontal balance-wheel, weighing _fourteen tons_, which runs on a step of five inches diameter, and makes from seventy-five to one hundred revolutions in a minute. About one hundred tons of iron are rolled in this machine in a month; yet the wheel has sometimes been used from three to five weeks without inconvenience, before the soapstone has been renewed. The superintendent thinks, however, that it ought to be more frequently employed.

“The use of soapstone was discovered at Lowell. It has been said never to fail in producing the desired result when applied to machinery which had began to be heated, even in those cases when nothing else could be found that would answer the purpose.”—_Silliman’s Journal_, xiii. 192.

6. _On peculiar Physical Repulsions, by_ M. Saigey.—I intend to give in this bulletin the description of a very simple apparatus, by means of which I have made many experiments, which have conducted me to the following results:—

i. All bodies exert between themselves a feeble repulsive action in ordinary circumstances. The repulsion between bismuth and [p456] antimony and the poles of a magnetic needle, is a case of this general law, and is not due to magnetism. Nor is it magnetism which occasions the direction of needles formed of other substances than iron, announced lately by M. Becquerel.

ii. A very marked attraction may be observed between a cold and a heated body, or between two bodies of different temperature, whether screens be interposed or not.

iii. The metallic plates in the Cabinet de Physique de Paris, intended for the repetition of M. Arago’s experiments on magnetism by rotation, contain more or less of iron capable of attracting a very mobile magnetic needle. These plates, and those of M. Arago, were made by the same person and from the same materials.

iv. I believe that, in many cases, results obtained without the appreciable developement of magnetism or electricity, have been attributed to these powers; and from well-proved experiments I shall deduce new results relative to the diurnal variation of the needle, the direction of the plumb-line and the density, temperature and attraction of the planetary masses.—_Bull. Univ._ A. viii. 287.

7. _On the Magnetic Effects of Metals in Motion_.—M. Seebeck has endeavoured to determine the effects of various metals in diminishing the oscillations of a magnetic needle 2-1/8 inches in length, and suspended by a silk fibre three lines distant from and above the plates. The oscillations were counted from an amplitude of 45° to 10°.

116 oscillations above a plate of marble
112 layer of mercury 2 lines in thickness.
106 plate of bismuth 2 "
94 platina 0.4 "
90 antimony 2.0 "
89 lead 0.75 "
89 gold 0.2 "
71 zinc 0.5 "
68 tin 1.0 "
62 brass 2.0 "
62 copper 0.3 "
55 silver 0.3 "
6 iron 0.4 "

It is also stated that he has found, from experiments, that by alloying such metals as are magnetic, like iron, nickel, and cobalt, with other metals, which like antimony diminish the magnetic force, alloys are obtained entirely neutral in their effects; thus the alloys formed by four of antimony with one of iron, three of copper with one of antimony, and two of copper with one of nickel, produce no diminution of the number of oscillations, these amounting to 116 as with the plate of marble. These three alloys are, therefore, the best for the manufacture of compasses, those of copper and nickel being the most malleable.—_Annal. des Phy. 1826. Bull. Univ._ A. viii. 136. [p457]

8. _Duration of the Effects of Light upon the Eye_.—M. Plateau of Liege has endeavoured to determine the length of time during which the impression of certain luminous rays upon the eyes remains; and has given the following results:

Flame 0″.242 Ignited Charcoal 0″.229 White 0″.182 Blue 0″.186 Yellow 0″.173 Red 0″.184

9. _On the Measurement of the Intensity of Light, by_ M. Peclet.—A very usual photometrical process is to interpose an opaque body between a white screen and the two lights to be measured, and to move the latter until the shadows produced are of equal intensity; the intensity of the lights being then as the square of their distances from the shadows they illuminate. Sometimes a translucent body, as unpolished glass or oiled paper, is used in place of an opaque one, the shades produced by transmission being observed.

In both these methods, the apparent intensity of the shadow varies with the position of the observer. If the shadows are equal when observed from a point perpendicular to the white screen at the middle of the distance of the two shades, they will be no longer so on removing from that position, and the shadow nearest to the observer will always appear the darkest. These apparent variations are greater as the shadows are farther apart, or with reflected shadows as the screen is smoother, or with transmitted shadows as the interposed obstacle is more diaphanous.

The explanation given of this fact is, that unpolished opaque bodies, like paper, plaster, &c. never disperse the light incident upon them, in an uniform manner, more rays passing in the direction in which regular reflexion would take place, than in any other. Hence, when two equal shadows are produced upon such a surface, either by two equal lights at equal distances, or by two unequal lights at unequal distances; the shadow nearest to the observer must necessarily appear deeper than the other, because it is enlightened by the nearest light, the rays from which are reflected in greatest abundance away from the observer; and, on the contrary, the shadow further from the observer should appear lightest, because the rays which fall on it from the furthest light are reflected in greatest abundance towards the side on which the observer stands. The reason, also, why the effect is greater as the shadows are further apart is evident; and why in every case it is reduced to nothing when the observer is in a plane perpendicular to the screen and equidistant from the two shadows.

From these facts and explanations it may be concluded, that, in all photometrical measurements by reflected shadows, the screens should have all smoothness removed from them, and the two [p458] shadows brought as near together as possible, and even made to touch or over-lap; or that, when this cannot be done, the observation should be made from a point equidistant from the two shadows. As to the shadows by transmission, the apparent variations of intensity are so great for small changes in the position of the eye, as to render the method altogether inapplicable.—_Bull. Univ._ A. viii. 248.

10. _On the apparent Decomposition of White Light by a Reflecting Body when in Motion_.—The following experiment is described in the MSS. of M. Benedict Prevost and published by M. P. Prevost. A ray of solar light being introduced into a darkened chamber, is to have a square piece of white paper about two inches in the side, passed across it perpendicularly to the direction of the ray. The light reflected by the paper, instead of being white, will present a small white central portion, surrounded by the seven principal colours, nearly in the order of the prismatic spectrum. When a red surface is used instead of a white one, the decomposition of the light is still more complete. When the paper has a slight blue tint, the effect is less perfect than with the white paper. With a black surface no colours appear, but a sort of smoky shade towards the middle. A single passage of the paper is sufficient, but it is necessary that it pass entirely through the ray, no part remaining in it.—_Bib. Univ._—_Bul. Univ._ A. viii. 248.

11. _On the Barometer_.—The following are conclusions at which M. Bohnenberger has arrived relative to the barometer: i. The surface of mercury in a tube 14.5 lines in diameter, is slightly rounded at the edge; but, at the distance of two lines from the glass, capillary depression disappears, and the surface is level. ii. The mercury in a tube 5.8 lines in diameter is convex over the whole surface, the depression being .035 of a line. iii. The depression is generally less in a vacuum than in the air, so that a syphon barometer gives results too high, and the more so as the tube is smaller. iv. Barometers constructed with tubes five lines in diameter, do not require tapping to cause them to assume their proper height; and comparatively slight blows easily make the mercury rise too high in tubes of a smaller diameter.—_Annal. der Phys. und Chem._

12. _Easy Method of reducing Barometrical Observations to a Standard Temperature, by_ S. Foggo.—The expansion of mercury deduced by the different philosophers who have examined it, is given below; omitting the results of Sir G. Shuckburgh, as being rather too far from the mean of the others.

Expansion of mercury, from 32° to 212° F.

De Luc 1-56th } Lavoisier and Laplace 1-55.22th } Halstrom 1-55th } mean, 1-55.43th. Dulong and Petit 1-55.5th }

[p459]

For 1° of Fahrenheit’s scale, this is equal to 1/9977.4, or .00010023: which may be called one ten-thousandth, without the most trifling error in practice. The barometric column may, therefore, be reduced to the standard temperature of 32° F. by the following simple rule, which will make a table unnecessary. _Before the first three figures of the observed height place two cyphers, multiply by the temperature of the mercury −32°, and subtract the product from the observed height_. Example; barometer 30.597, temperature of mercury 74°.

74° − 32° = 42°.00305 × 42 = .128 and 30.597 − .128 = 30.469 the correct height.

When the temperature of the mercury is lower than 32°, the temperature is to be subtracted from 32°, and the product, obtained as before, is to be _added_ to the observed height. Thus, let the barometer be as before, and the temperature 15°: then 32° − 15° = 17°; .00305 × 17 = .052, and 30.597 + .052 = 30.649, the correct height.—_Jameson’s Journal_, 1827, p. 378.

13. _Diamond Lenses_.—I see by the last number of the Journal of Science and the Arts, that Mr. Varley has made a Diamond Lens, and also a single microscope with such motions as enable the observer to follow an animalcule in a diagonal direction. It is very odd, but this is precisely my plan for a microscope, which I drew up about four years ago; and as I could not get any optician to undertake it, I sent it to the Society of Arts, and recommended them to offer a premium for the best diamond lens, but they returned it. I have had a microscope of this sort (made by W. and S. Jones, Holborn) about a year and a half, and it answers the purpose completely; as a person not at all used to microscopes may use a lens of 1/60 inch focus and find a small object with it, and bring any part of it into the field of view with the greatest facility, and follow the motions of an animalcule in a diagonal direction. There are some alterations and improvements, which I have since made, that have rendered it a very complete microscope; a drawing of which I could send you, if you think it would be acceptable.

I am, Sir, yours, &c.
_Tringham, Norfolk, July_ 9_th_, 1827. G. DAKIN.

14. _Sapphire Lenses for Single Microscopes_.—As it may justly be feared that, notwithstanding the incontestable superiority of diamond lenses, the cost and difficulty attendant on their production will enhance their value beyond the reach of the public, Mr. A. Pritchard, No. 18, Pickett Street, has applied himself with indefatigable perseverance to the formation of _Sapphire Lenses_. The valuable experiments of Dr. Brewster have determined that the sapphire possesses a stronger refraction than any other substance capable of giving a single image (diamond excepted), [p460] while its dispersive power is only 0.026 compared to water as 0.035. Thus if a sapphire is ground in the same tool which will form a lens of glass of the 1/60 inch focus, it will come out about the 1/100 inch focus; being almost double the power of the glass in linear amplification, and more than double in superficial; in which latter mode of estimation the powers of the glass and sapphire may be rated at 360,000 to 1,000,000. The faint blue tinge of the sapphire is not felt in thin small lenses formed of this substance, which thus come next in order to diamond ones, and form an excellent _pis aller_ for those who cannot come at the latter. Many of our first microscopists are already in possession of them, and have honoured them with their unqualified approbation.

There is a property possessed by small single lenses formed by precious stones, which is worthy of being commented on: viz. They can be burnished fast into brass rings, and thus safely cleaned and removed at pleasure from one setting to another. The cohesion of glass is too slight to permit this operation, during which it is almost sure to burst into shivers.—C. R. G.

15. _On a Method of Securing and Preserving the Rowing Pins in Boats_.—Dear Sir,—To remove a petty inconvenience of hourly occurrence, by some simple contrivance, is often productive of a greater mass of advantage than an invention of greater splendour, and of apparently more extensive utility.

In the accompanying drawing, you have a plan for preserving that indispensable requisite in a boat, the towels, or rowing pins; the loss of which is not only very teasing, but often productive of serious inconveniences; while the practice of stealing them from each other forms a constant source of petty depredations, leading to perpetual quarrels among seamen in harbours. He who has been detained the better part of a day in the island of Sky, till half [p461] a dozen of these pins could be procured, well knows how to value that trifle, the neglect of which has caused the loss of his voyage, and might have led to that of his boat and his life also.

Fixed towels cannot well be used when boats are to be hoisted in alongside, as they are subject to be broken; and they are often inconvenient in getting in water casks, as well as in many other cases. Hence, pins capable of being unshipped are preferable. These are frequently lost, and the want is not always discovered till it cannot be replaced; or else it is not replaced without loss of that time which is often so valuable at sea. Very often, also, the delay of even a minute is rendered inconvenient or even dangerous; when the boat is dragging alongside by the painter in a heavy sea, and the vessel is either drifting or standing on.

The drawing requires little explanation. By pulling at the lower pin, the two upper are fixed at once, and on being unshipped they hang secure from loss; while the lower one serves us a spare towel, should any be broken. As not one boat in twenty thousand is provided with this invention, which is indeed scarcely known, it will not perhaps be found undeserving a place in your Journal.—

I am, &c. J. M.

16. _Cold Injection for Anatomical Preparation_.—If a mixture of varnish and vermilion has a small quantity of water mixed with it, it soon sets and becomes hard. This affords an excellent composition for anatomical injection, being very beautiful and very penetrating, (so much so, that it frequently returns by the veins,) and requiring no heat to be applied to the subject. The writer of this article frequently had, in the course of his medical education, the office of preparing this injection, of which he has, however, unfortunately forgot the proportions, and the particular nature of the varnish. It was, he thinks, a spirit varnish; the water was not mixed until the instant the injection was wanted, when it was well worked up with the syringe, and immediately thrown in; in the course of a night it would have set beautifully. This particular kind of injection was invented by an American anatomist of the name of Ramsay, and preserved as a valuable secret by him for the exclusive use of his own dissecting room. The proportions, &c. of the ingredients will soon be attained by a few experiments.

II. CHEMICAL SCIENCE.

1. _Extraordinary Experiments on Heat and Steam by_ Mr. Perkins.—“I discovered that a generator at a certain temperature, although it had a small crack in it, would not emit either water or steam. This fact I mentioned to a very scientific friend, who questioned its accuracy, and to convince him I tried the experiment; but he concluded that the expansion of the metal must have closed the fissure. To remove every doubt, I proposed to drill a small [p462] hole through the side of the generator, which was accordingly done. After getting the steam up to a proper temperature, I took out the plug, and although we were working the engine at thirty atmospheres, nothing was seen or heard to issue from the plug-hole; all was perfectly quiet: I next lowered the temperature by shutting the damper, and opening the furnace door; a singing from the aperture was soon observable, and when a coal was held before it, rapid combustion ensued; nothing, however, was yet visible: but as the temperature decreased, the steam became more and more visible, the noise at the same increasing, until finally the roar was tremendous, and might have been heard the distance of half a mile. This was conclusive. I should mention that, at the aperture, the iron was red-hot.” “The hole was one _quarter of an inch_ in diameter.”

“The experiment affords some data towards answering the question, at what distance from the heated metal the water remained, when under the pressure of thirty atmospheres; we may safely aver that it exceeded one-eighth of an inch.”—_Silliman’s Journal_, xiii. 46.

2. _On the Use of feeble Electric Currents, for effecting the Combination of numerous Bodies, by_ M. Becquerel.—A highly interesting memoir on this subject is inserted in the thirty-fifth volume of the _Annales de Chimie_, the intention of M. Becquerel being to show that electro-chemical powers may be used not only for the decomposition and analysis of bodies, but also for the production of new compounds.

The facts described in the paper are commenced by one intended to illustrate future reasoning, by shewing what takes place when a very feeble electric current traverses a metallic circuit, interrupted in one part by a neutral solution, into which the two extremities of the wires forming the circuit are immersed. Two small copper wires were connected together by loops, and the two free ends joined to the ends of a galvanometer wire; the circuit was then cut in one place, and the extremities immersed in a solution of chloride of sodium. Then, if one of the loops be raised to a red heat by a spirit lamp, an electric current is produced, the heated loop furnishing negative electricity. Now if the ends plunged in the saline solution are terminated by platina or gold wires, _no current_ of electricity is observed; with silver terminations, the current is very feeble; but with wires of zinc, lead, iron or tin, the current is very energetic. These remarkable effects, highly important in the phenomena hereafter to be considered, are no way connected with the conductibility of the metals; for lead and zinc, which are the worst conductors, are those which, with the copper, produce the most powerful effects. The current ceases altogether as soon as the lamp is removed.

As the zinc, copper, lead, and iron, belong to the class of oxidable metals, M. Becquerel concludes, from this experiment, that [p463] when very feeble electricities are generated in any point of a metallic circuit, interrupted by a saline solution, _a current of electricity is formed or not, according as the two similar metallic terminations, which dip into the solution, belong to an oxidable or non-oxidable metal_. If the saline solution be replaced by an acid, _then_ a current will be obtained, though platina wires be used; because that kind of fluid does not interrupt the current.

With respect to the production of new compounds by electro-chemical powers, very much depends upon the strength of the power employed, and M. Becquerel only pretends, as yet, to indicate a new field of research, and not to point out the precise paths to be pursued. Two methods may be adopted. As an illustration, let a tube, from 4 to 8 hundredths of an inch in diameter, be bent into the form of the letter U, and place a plug of amianthus at the bend, to prevent the mixture of the fluids in the limbs: into one leg put a mixture of deutoxide of copper and solution of the sulphate of copper, the former will fall to the bottom; into the other put a saturated solution of common salt, and also an excess of the dry substance, then communicate the two fluids by a plate of copper. Very shortly the end plunged in the sulphate will be covered with metallic copper, and the acid set free will act upon the oxide of copper below and form more sulphate, so that a set of decompositions and recompositions will occur, and ultimately comparatively large crystals of copper will be obtained.

In the other branch of the tube, a portion of the salt will be decomposed, the muriatic acid will act upon the copper, which is oxidised in consequence of its positive state, and will probably produce an oxychloride, which will combine with the chloride of sodium, and then octoedral crystals will be formed on the plate of copper. The effects are produced either with or without access to air.

When the crystals are well dried and inclosed in a tube hermetically sealed, they suffer no change; but they are decomposed by water into chloride of sodium and submuriate of copper.

If the voltaic experiment be continued for one or two months, the crystals, from being colourless and limpid, become violet, and ultimately acquire an emerald green hue, still remaining transparent. If the chloride of sodium side be tested, it will be found that soda is evolved during the experiment. A piece of copper simply immersed in a solution of common salt, produces nothing more than a submuriate of copper, which precipitates.

_With silver_.—If a similar tube to that described have both limbs filled with a solution of salt, a platina wire introduced into one limb, a silver wire into the other, the extremities of the wire connected so as to form a voltaic circuit, and the whole left for some months, in about fifteen days crystals will be observed on the silver wire; these will gradually increase and assume a rhomboidal form. They have not yet been particularly examined, but [p464] are known to be unchanged by water: during a long experiment they change colour, becoming, first, violet, then blue.

Experiments similar to that with the copper, when repeated with the same solutions, &c., but the substitution of plates of lead and tin for the copper plates, produced crystalline double chlorides of these metals and sodium.

Muriate of ammonia being substituted for common salt in these experiments, another series of double compounds was obtained with copper, silver, lead, and zinc.

A double chloride of barium and lead was formed slowly in a similar way.

When a solution of the iodide of potassium or sodium was used instead of the solution of salt, then double iodides were obtained: thus with lead rather a rapid formation of silky crystals occurred upon the lead, which, when examined by water, were decomposed, producing iodide of lead and solution of iodide of potash or soda. A tube two or three times the diameter of the former may be used for the experiment.

The second method of producing new combinations by weak electro-chemical powers, depends upon the electro-motive action, which is caused whenever a metal touches the oxides, or an oxide of another metal. If an oxide of a metal, a plate of metal, and a liquid be put into a tube closed at one extremity, there will be an electro-motive action of the metal with the oxide, and of the liquid with both these bodies; and the chemical effect will be according to the resultant of these three forces, which can only be ascertained by experiments.

As an illustration of the effects thus produced, three tubes, from eight to twelve hundredths of an inch in diameter, were prepared, a little protoxide of lead being put into one, deutoxide into the second, and peroxide into the third; solution of muriate of ammonia and a plate of lead were then added to each tube. After a time, lead was precipitated in the first tube, very slight chemical changes took place in the second, but a large quantity of double chloride of lead and ammonia crystallized upon the lead in the third, in the form of needles. Thus very different effects were produced, according to the state of oxidation.

Solution of salt gave similar results with the oxides of lead and lead.

The oxides of copper, with solutions of alkaline muriates, gave curious results. With muriate of ammonia, crystals were produced of considerable size, and different to those obtained by the former process. In this experiment, the black and anhydrous deutoxide of copper gradually acquired a blue colour, as if a hydrate were formed under the influence of the feeble electric current formed by the arrangement.

Copper, its deutoxide, and solution of corrosive sublimate, produced a double chloride, crystallizing in plates, and possessing a metallic lustre. [p465]

3. _Crystallization of Metallic Oxides_.—If a solution of nitrate of copper, mingled with very fine charcoal powder, or even deutoxide of copper, be put into a similar tube to that described in the last article, then a plate of copper be introduced and the vessel closed up, in about fifteen days small red transparent octoedral crystals of protoxide of copper will be formed on the plate of metal. Other metals have been subjected to similar experiments, but probably have not yet remained long enough under action.—_Ann. de Chimie_, xxxv. 113.

4. _On Bromine, by_ M. A. de la Rive.—M. de la Rive has remarked a curious fact respecting the conducting power of fluids for electricity in the habitudes of bromine and water. He found, in the first place, as M. Balard had stated, that pure dry bromine did not conduct the electricity of a voltaic battery, consisting of sixty pairs of plates very strongly charged, a delicate galvanometer being the test: a similar experiment was then made with pure water, the water being contained in a glass capsule, and communicated with the battery and galvanometer by platina wires[129], and the deviation of the needle was scarcely sensible. Some other experiments induced M. de la Rive to believe, that water perfectly distilled and put into vessels made of substances absolutely unacted upon, would not conduct any portion of electricity: the purer the water, and the more unchangeable the substance of the vessel, the feebler does the conducting power become, until at last it is insensible.