Chapter XVI: TECHNOLOGY.--Apparatus for the Manufacture of Acetylene (2)

The rowboat Fox, of the port of New York, manned by George Harbo, thirty-one years of age, captain of a merchantman, and Frank Samuelson, twenty-six years of age, left New York for Havre on the 6th of June. Ten days later the boat was met by the German trans-atlantic steamer Fürst Bismarck proceeding from Cherbourg to New York. On the 8th, 9th and 10th of July, the Fox was cast by a tempest upon the reefs of Newfoundland. The two men jumped into the sea, and thanks to the watertight compartments provided with air chambers fore and aft, it was possible for them to right the boat; but the unfortunates lost their provisions and their supply of drinking water. On the 15th they met the Norwegian three masted vessel Cito, which supplied them with food and water. The captains of the vessels met with signed the log book and testified that the boat had neither sail nor rudder. The Fox reached the Scilly Islands on the 1st of August, having at this date been on the ocean fifty-five days. It arrived at Havre on the 7th of August.

Cost what it might, the men were bent upon reaching this port in order to gain the reward promised by Mr. Fox, of the Police Gazette. Thanks to the wind and a favorable current, they made 125 miles in 24 hours. One slept three hours while the other rowed. Their skins and faces were tumefied by the wind, salt water and sun; the epidermis of their hands was renewed three times; their legs were anchylosed; and they were worn out.

The boat was 18 feet in length, 5 in breadth, and 23 inches in depth, and carried a small kerosene stove for cooking.--L'Illustration.

* * * * *

THE WASTE OF SHIPPING.

Burdensome as are the restrictions imposed upon shipowners by legislation, considerable justification is found for them when we compare the percentage of British vessels lost at sea with that of foreign-owned vessels. The great shipping countries, that is, those which have more than 1,000,000 tons afloat, are the United Kingdom, the British colonies, the United States of America, France, Germany and Norway. Of these six the United Kingdom suffered the least comparative loss in its mercantile fleet in 1895. Under all the heads of abandoned at sea, broken up or condemned, burnt, collision, foundered, lost, missing and wrecked, the total loss was 2.99 per cent. of the vessels owned and 2.36 per cent. of the tonnage owned. No other of the countries named has less than 3 per cent. of loss, while only the British colonies have less than 4, as the subjoined table shows.

TOTAL LOSSES OF STEAM AND SAILING VESSELS IN 1895.

----------------------------------------------------------------+
| Vessels Owned. | Percentage Lost. |
|------+-----------+-------------------+
Flag. | | | Vessels | Tonnage |
| No. | Tons.[1] | Owned. | Owned. |
-------------------------+--------------------------------------+
United Kingdom. | 9227 |12,117,957 | 2.99 | 2.36 |
British Colonies. | 2307 | 1,124,682 | 3.38 | 3.70 |
United States of America.| 3220 | 2,164,753 | 4.72 | 4.06 |
French. | 1164 | 1,094,752 | 6.01 | 4.02 |
German. | 1730 | 1,886,812 | 6.76 | 4.38 |
Norwegian. | 3041 | 1,659,012 | 7.43 | 6.46 |
-------------------------+------+-----------+---------+---------+

[Footnote 1: Gross tonnage for steamers; net for sailing
vessels.]

When we turn from the contemplation of the complete fleets, and differentiate between steam and sail, we find that the United Kingdom no longer holds the premier position, being surpassed, as regards steam, both by the colonies and by the United States. Steam vessels are safer than sailing craft all over the world, partly, of course, because their average age is less. The losses they suffered last year are as follows:

TOTAL LOSSES OF STEAM VESSELS IN 1895.

-------------------------+--------------------------+-------------------+
| Vessels Owned. | Percentage Lost. |
+--------------------------+---------+---------+
Flag. | | | | Vessels | Tonnage |
| No. | Net. | Gross. | Owned. | Owned. |
-------------------------+------+---------+---------+---------+---------+
United Kingdom. | 6446 |5,993,666|9,695,976| 3.33 | 2.13 |
British Colonies. | 874 | 329,845| 542,025| 1.72 | 1.69 |
United States of America.| 626 | 660,784| 920,672| 2.23 | 1.93 |
French. | 571 | 467,553| 903,105| 4.20 | 3.42 |
German. | 953 | 910,567|1,343,357| 3.04 | 2.64 |
Norwegian. | 586 | 285,349| 446,384| 2.56 | 2.87 |
-------------------------+------+---------+---------+---------+---------+

The United Kingdom here stands third in the list, and curiously it only stands second under the head of number of sailing ships lost, while it is first as regards sailing tonnage lost. The sailing tonnage of the United Kingdom is only about 20 per cent. of the total, while in the colonies it is about 52 per cent. The following are the figures:

TOTAL LOSSES OF SAILING VESSELS IN 1895.

-------------------------+-----------------+-------------------+
| Vessels Owned. | Percentage Lost. |
+-----------------+---------+---------+
Flag. | | | Vessels | Tonnage |
| No. | Tons. | Owned. | Owned. |
-------------------------+------+----------+---------+---------+
United Kingdom. | 2781 |2,421,981 | 4.53 | 3.27 |
Colonies. | 1435 | 582,657 | 4.39 | 5.56 |
United States of America.| 2594 |1,244,081 | 5.32 | 5.63 |
French. | 593 | 191,647 | 7.76 | 6.83 |
German. | 777 | 543,455 | 11.33 | 8.66 |
Norwegian. | 2455 |1,212,628 | 8.59 | 7.78 |
-------------------------+------+----------+---------+---------+

The losses of sailing vessels are very serious among the Continental nations, especially in Germany, where more than one in nine was lost or condemned last year. This is greatly due to the fact that our old ships are largely sold to the foreigner when they will no longer comply with legislative conditions of this country. We break up a few, but only 0.75 per cent., against 1.75 per cent. for Norway and 2.5 per cent. for France and Germany. We are more chary of breaking up our steamers; last year only 0.46 per cent. met this fate here, 0.34 per cent. in the colonies, 0.32 per cent. in the United States, 0.86 per cent. in France, 0.31 per cent. in Germany, while Norway did not lose a single steamer in this way.

Turning now to the present year we find that in the first quarter the vessels lost, condemned or reported missing before August 7 were, according to returns made out by Lloyd's Register of British and Foreign Shipping, 282 vessels, of an aggregate of 195,480 tons. These figures are respectively 23 per cent. and 24 per cent. of the total losses last year, thus showing a favorable beginning, for the winter losses are naturally the heaviest. The materials of the vessels lost were: Steel, 24 vessels of 40,474 tons; iron, 74 vessels of 78,314 tons; and wood and composite, 184 vessels of 76,692 tons. The United Kingdom shows best under the heads of total losses and losses of sailing vessels, but in steamers it actually comes last among the six nationalities we have selected for comparison. It must be remembered, however, that the British fleet is large enough for a very fair average to be attained in three months, while in all other fleets a single loss, more or less, makes a great difference to the figures of merit. The steam tonnage of the United Kingdom is more than seven times greater than that of Germany, which is our chief competitor. In sailing tonnage we do not hold this immense superiority, our amount being only about double that of the United States and of Norway respectively.

When we examine the various causes of loss of vessels at sea, we find nearly 43 per cent. of the tonnage under the head of "wrecked," which includes vessels lost through stranding, or through striking rocks, sunken wrecks, etc. Next come 22 per cent. broken up or condemned; 14 per cent. lost, missing; 8 per cent. lost by collision; 4.3 per cent. burnt; 5 per cent. abandoned at sea; and 3.6 per cent. foundered. The following table shows the mercantile marine of the world, according to Lloyd's Register, at the end of March, 1896:

Flag. Steam and Sailing
Vessels Owned.

No. Tons. British. /United Kingdom. 9227 12,117,957 \Colonies. 2309 1,124,682 America, United States of. 3220 2,164,753 Austro-Hungarian. 309 304,970 Danish. 812 356,714 Dutch. 458 446,861 French. 1164 1,094,752 German. 1730 1,886,812 Italian. 1239 778,941 Norwegian. 3041 1,659,012 Russian. 1086 487,681 Spanish. 748 554,238 Swedish. 1432 497,877 Other European countries. .... ......... Central and South America. .... ......... Asia. .... ......... Other countries. .... .........

--Engineering.

* * * * *

NEW METHODS OF BUILDING CONSTRUCTION AT PARIS.

During recent years an interesting change has been gradually brought about in the various methods of building construction employed in France, and more especially at Paris, where the size and importance of public buildings and the many-storied houses divided up into flats necessitate special systems of construction, which possess the advantages of combining economy in cost with strength and durability. Parisian architects and builders, although far from approving the extremes to which their American confrères go in the employment of iron for the construction of their somewhat exaggerated sky-scraping buildings, in which the style of architecture employed is often scarcely logical or consistent with the modern methods of construction, are nevertheless obliged to own to the necessity and the utility of employing iron in moderation for the framework of their buildings. Up to the present the use of iron in its ordinary form has chiefly been confined to floors, partitions, and roofs, where, as a rule, its presence is masked by coverings of cement, wood, or stone, except in recent examples of the new style of buildings destined for brasseries or drinking halls, where the iron construction is left visible, and emphasized by means of bronze or color painting and mosaic work, or, again, in the few examples of well known work where the architect has endeavored to obtain a decorative effect by means of iron lintels and columns. But where the use of iron is fast finding favor at Paris is in its employment in combination with other materials such as cement or concrete, and in a special form known as the cement armé systems, in which iron or steel is employed in the form of thick wire, trellis, or light bars embedded in cement or concrete. This method of construction, of which there are three different systems, has for some time been employed in the construction of various buildings of more or less importance, and has given proof of its strength and practical use as well as its advantages when employed for floors, partitions, walls and roof, both as regards its conveniences for internal arrangements, its economy, and as regards the manner in which it lends itself to modern schemes of polychrome decoration.

Two of these systems have been employed by the architect of the new building now being constructed in the Rue Blanche for the Society of Civil Engineers of France. The third system is much employed by M. De Baudot in various buildings designed by this architect, an advocate of rational construction and design and the logical employment of modern building materials. It will be interesting to examine the merits of each system as employed in these buildings, together with any other points of construction worthy of remark.

The building for the Society of Civil Engineers is remarkable from several points of view as regards construction and the arrangement of plan. The façade and plans will appear in the Building News as soon as the work is completed, and will form an interesting subject for comparison with the building recently completed for the English Society of Engineers, and with that about to be commenced at New York for the American Society.

Before entering into a detailed description of the system employed, a summary idea of the plan and general scheme of construction will not be uninteresting. The architect, M. Fernand Delmas, has endeavored to construct the building on economical lines, employing to a large extent iron and those modern materials which have been tried and found fitting as regards suitability and economy; the building will cost £22,000, and it has been made a sine qua non that all the contractors shall be members of the Society of Engineers.

The length of the façade is 100 ft.; the total depth of the building is nearly equal to the frontage; the height from pavement to cornice is 60 ft. The façade is built of solid stonework throughout its length and height. The thickness of the masonry is 24 in. at the lower stories and 18 in. at the upper portion. The façade wall is really the only portion of solid masonry work in the whole building, and forms a decorative mask to the body of the building, which is constructed of a framework of iron. The chief supports of the building proper consist of four framed iron uprights, 16 in. by 16 in. rising from the basement to the roof. These uprights are solidly trussed and held together at the floor levels by strong iron girders supporting the iron joists of the upper floors and the light partitions which divide up each story. This system is at once economical and practical. The whole building is thus self-supporting, and the thick walls which would otherwise be necessary for carrying the upper floors are thus avoided.

The façade wall is built according to the system always employed at Paris, and is formed of blocks of stone roughly cut at the quarries to the outside dimensions of the proposed moulding and decorative work. As soon as the whole front is erected the work of cutting it into shape will commence, the mouldings, pilasters, and all carving work being done while the interior is being prepared. The buildings at Paris are by this means erected much more rapidly than when the stone is dressed or moulded before being put into place. Greater facilities are thus given for studying the general ensemble of the façade and the proper scale to be given to the mouldings and decoration. The stone is as a rule soft when first from the quarries, but becomes hard and durable after dressing and exposure to the air. The courtyard wall of the building is formed of light brick or metallic fillings between the iron uprights and the party walls.

The ground floor comprises a large entrance hall or vestibule, 40 ft. by 44 ft., forming, with the cloakroom, the principal staircase, the rooms for the concierge, and the area, the whole front of the building. This large vestibule is vaulted over by means of one of the systems of cement armé to be described. The floor is constructed on another similar system, and will be paved with mosaic work. The ground floor of the courtyard will be occupied by the conference hall, 50 ft. by 50 ft., to hold 300 seats. An annex, 50 ft. by 20 ft., adjoining this hall, will open on the same by a large arched bay, and may be separated from the larger hall by means of a special system of wooden soundproof roller shutters. The floor of the large hall will be a movable one, to be raised or lowered by an ingenious system of hydraulics, and capable of being placed in an inclined position for conference meetings, or raised to a horizontal position for ball room purposes.

The entresol floor will comprise a large room for meeting, smoking and conversation rooms, and a reading room, to be used as a club for the members of the society. The first floor will contain the offices of the society, a large committee room, and all conveniences. The second floor will be devoted entirely to the purposes of the important library, comprising the library proper, a room 45 ft. by 25 ft. by 17 ft. high, rising to the ceiling of the low story above, and lighted by a large semicircular bay at either end: the surrounding rooms of the height of the second floor will be destined for the librarian, catalogues, drawing office, and library offices. The third floor will be devoted entirely to the purpose of storing the books of the library, in low rooms communicating by means of the gallery overlooking the library below, which will be crossed by means of a light, iron bridge. The bookcases will be suspended from the upper floor, and will be arranged in vertical tiers hung on rollers, after the system employed at the British Museum. The roof story will be divided up into an apartment for the chief secretary, and reached by a private staircase from the ground floor. The large basement, occupying the whole of the ground surface of the building, will be used for storing the records of the society, and will contain the heating apparatus, stores, etc. A hydraulic lift will afford access to the landings of each floor. The chief feature of the façade, which is simple in style, is the wide arched bay, 24 ft. across, rising from the pavement to above the cornice; this bay will be filled in with an open decorative framework of wrought and cast iron.

Some of the most interesting points of the construction, besides the large use of iron, are the systems employed in the construction of the floor. The ground floor is built after the Coignet system, composed of light iron bars and cement; the first floor and its supporting pillars and arches is constructed after the Hennebique system of cement armé; the upper floors are formed of iron joists, filled in either with the system of light supports and plaster, much employed at Paris, or with terracotta fillings between joints. The roof is lined internally with agglomerated cork bricks, affording protection from excessive heat or cold, and the walls of the area will be lined with opaline, a vitreous material of a bluish white color, which in this case will insure cleanliness, and afford additional light; the lavatories and water closets will also be lined with the same material.

Speaking of the Hennebique system of cement armé, employed for the arches and floor of the first story, it will be interesting to illustrate the method by a few sketches, explaining the theory of this system, which has been put to practical proofs in a large number of buildings, chiefly for industrial purposes, in the north of France. The perspective section will give an idea of the construction as employed in the building for the civil engineers, a system which holds its ground well against its rivals of other methods of cement armé.--The Building News.

* * * * *

BELLEEK CHINA.

Belleek porcelain (frequently pronounced "Bleak" by those who do not know the derivation of the name) is a thin eggshell ware of great lightness and translucency, characterized by a creamy, or sometimes grayish, tint, and usually covered with a delicate pearly or lustrous glaze. It is in reality a variety of Parian ware, being formed in the same manner by the process called casting, or pouring diluted clay or slip of the consistency of cream into plaster moulds, which, by absorbing a part of the moisture from the portion of the liquid preparation in direct contact, retain a thin shell of partially dried clay after the superfluous contents are taken out. After standing a few minutes the thin cast can be liberated from the mould. The thickness of the walls, of course, depends upon the length of time the slip is allowed to remain in the mould before the surplus is removed. By this ingenious method cups, saucers and other forms of ware can be made almost as thin as an egg shell or a piece of heavy paper, and after being allowed to become thoroughly dry can be safely burned in the kiln. It can readily be understood that it would not be possible to make such fragile pieces by the usual processes with plastic clay, which must be of the consistency of putty or dough, on the potter's wheel or by pressing in moulds.

Belleek ware was first made at Stoke upon Trent by the eminent potter William Henry Goss, who invented the body or composition some thirty-five years ago; but it was not then known by this name. Soon after its introduction Messrs. McBirney & Armstrong induced some of Mr. Goss' workmen, including his manager, William Bromley, to join them at their porcelain works, then recently started (in 1863) in the town of Belleek, County Fermanagh, Ireland, and the art was established so successfully there that the name of the village was given to the ware which has since become so noted. The distinguishing characteristic of this beautiful product is its lustrous glazing, which varies in form from white to yellow and through graded tints to a dark leaden hue.

Mr. Goss has continued to manufacture this dainty variety of porcelain until the present time, and his factory has become one of the most noted in the British empire. Among the most popular of his productions in this body are loving cups and little cream jugs, cups and saucers, and fairy tea sets embellished with beautifully colored crests and coats of arms of the different English cities and of prominent personages, such as Queen Elizabeth, Sir Walter Raleigh, King Henry of Navarre, Queen Victoria, the Prince of Wales, Shakespeare, Sir Walter Scott, and Robert Burns.

Of more interest, perhaps, to Americans are the porcelain tumblers which have just been produced at the same factory, bearing on the front a faithful duplication in blue and yellow enamels of the insignia of the society of Sons of the Revolution, which were made at the suggestion of a member of the society in Pennsylvania. The soft, satiny Belleek body seems to be particularly well adapted to show off to advantage the rich designs of these badges, and this suggestion will doubtless be followed by other patriotic hereditary societies in the United States.

John Hart Brewer, of Trenton, first attempted the manufacture of Belleek ware in this country. He commenced his experiments in this line in 1882, and in the following year brought over from England William Bromley and his son from the Belleek works in Ireland. Subsequently the elder Bromley joined the Willets Manufacturing Company, of the same place, and introduced the manufacture of eggshell porcelain there, and at the present time there are no less than five or six establishments in Trenton where the same class of ware is made.

Among many specialties recently introduced is a new style of decoration which has been worked out by Miss Kate Sears, a Kansas girl who studied modeling in Boston. Going to Trenton for the purpose of pursuing her studies in this direction, one day in 1891, while engaged in working over the wet Belleek, the idea of carving delicate designs in the dry clay occurred to her, and after conducting a series of experiments her efforts were crowned with success. The process of modeling which Miss Sears has originated is as follows: A vase or other piece which has been formed in the wet clay and dried is taken before it has been in the kiln, and with knives or other tools the design is cut or chiseled so as to leave the background as thin and transparent as possible when finished. As the dry Belleek, besides being thin, is extremely brittle, and crumbles easily, the carving is an exceedingly difficult operation. It is necessarily a very slow process, since at any moment the knife is liable to cut through the wall and ruin the piece.

The result of this process is a clear cut, chiseled effect, which cannot be obtained by moulding or casting, a moonlight effect of fairy like character, most beautiful in conception, and possessing marked originality. While sometimes several weeks are consumed in executing a single piece of the carved ware, Miss Sears has produced a large number of such designs, each one of which is a perfect work of art, reflecting credit upon the artist and the manufacturers.

The marks which appear on the various productions of Belleek porcelain are of considerable interest to collectors and admirers of this beautiful ware. Mr. Gross has adopted as a factory mark his family crest, a falcon rising ducally gorged, which is printed on each piece in black. The mark of the Belleek factory in Ireland, consists of the four Irish emblems, the watch tower, the hound, the harp of Erin, and the shamrock, and is printed on the ware in green or black. At the Etruria Pottery, formerly operated by Messrs. Ott & Brewer, now known as the Cook Pottery Company, the mark used on Belleek ware was a crescent bearing the name with the initials of the proprietors, "O. & B." The Willets Manufacturing Company uses for a factory mark on its decorated Belleek pieces the figure of a serpent looped in the form of a W, which is printed in red. On similar ware produced by the Ceramic Art Company is printed in red a design composed of a painter's palette and a circle inclosing the monogram C. A. C., while Messrs. Morris and Willmore, of the Columbian Art Pottery, employ a shield with the initials of the firm name, M. W.

The manufacture of Belleek ware was introduced into this country by English potters who had learned the processes at the potteries in England and Ireland, and we cannot, therefore, lay claim to originality so far as the product itself is concerned; yet, in a measure, the ware as made in America differs materially from the foreign in many respects, and has been developed in new directions, so that it has come to have distinctive characteristics of its own which entitle it to be ranked with original American productions. While our potters, perhaps, have not yet reached the high degree of elaborate modeling which characterizes some of the imported Belleek, they have already surpassed the foreign manufacturers in the simplicity and elegance of their forms and the artistic quality of their decorations, while in delicacy of coloring, in the excellence and lightness of body, the American products are not surpassed. A visit to the showrooms of the Trenton potteries will prove a revelation to those who still believe that no artistic china is made in this country.--Edwin Atlee Barber, in China, Glass and Lamps.

* * * * *

GOODMAN'S HATCHET PLANIMETERS.

The instrument we are about to describe is an improvement on the hatchet planimeter and is due to Prof. Goodman, of Leeds. One form of the instrument is intended for the measurement of areas of surfaces, and the other form for the measurement of the mean height of a figure such as an indicator diagram.

London Engineering, to which we are indebted for the cuts and copy, describes the instruments as follows: The method of using the two instruments is practically the same, but for the present we shall confine our remarks to the instrument for measuring areas. In order to familiarize oneself with the peculiar action of the instrument, it will be well to get a large sheet of paper on a drawing board or a large blotting pad, and holding the instrument vertical to the paper, grasp the tracing leg very lightly indeed between the forefinger and thumb of the right hand, with the hatchet toward the left hand, as shown in Fig. 1. Then by moving the tracing point round and round an imaginary figure and allowing the hatchet to go where it pleases, it will be seen that the hatchet moves to and fro along zigzag lines, and travels sideways--the side travel being nearly proportional to the area of the figure described by the tracing point. If the tracing point be too tightly grasped, the hatchet will not move freely, and, will have a side slip. When this occurs the side travel of the hatchet ceases to be proportional to the area traced out. A loose weight is hung on the hatchet to prevent this side slip, but as soon as a little skill is attained in the use of the instrument, this weight may be dispensed with.

When measuring the area of such a surface as that inclosed by the boundary line shown in Fig. 3, a point, A, is chosen somewhat near the center of the figure; the exact position is, however, immaterial. From the point, A, a line, AB, is drawn in any direction to the boundary; the tracing point of the planimeter is now placed at A, with the hatchet at X, Fig. 3, that is, with the instrument roughly square with AB. The hatchet is now lightly pressed in order to mark its position on the paper by making a slight dent, then leaving the hatchet free to move as shown in Fig. 1, the tracing point is caused to traverse the line, AB, and the boundary line in a clockwise direction, as shown by the arrows, returning to A via AB. The hatchet will now be found to have taken up a new position, Y, which must be marked by again pressing the hatchet to make a slight dent in the paper. If the figure under measurement be on a separate sheet of paper, the paper must now be revolved about the point, A, through about 180 deg. (by eye), using the tracing point of the instrument as a center, care being taken that neither the point nor the hatchet be shifted while the paper is being turned. The line, AB, will again be roughly at right angles to the instrument, but in the reverse direction (see dotted lines in Fig. 3). Again cause the tracing point to traverse the line, AB, and the boundary line as before, but this time in a contra-clockwise direction. The hatchet after this backward motion will take up the new position, X1, which may or may not coincide with X; if not, prick a central point between X and X1, as shown, then, of course, the distance of this point from Y is the mean side shift of the hatchet; this distance measured from the zero of the scale on the back of the instrument is the area of the figure in square inches. The scale is read in exactly the same manner as a geometrical scale on a drawing, the whole numbers being read to the right of the zero and the decimals to the left. The instrument does not profess to give results nearer than one-tenth of a square inch.

In some cases on large maps, for example, the figure cannot be turned round as indicated above; in that case the instrument itself must be turned round through 180° and two fresh dents, X¹Y¹, obtained; the area of the figure is then the mean of the two readings, XY and X¹Y¹.

When the area is large the instrument will move through a large angle, and consequently, if square with AB to start with, it will be considerably out of square at the finish. In such a case it is only necessary to see that the mean position of the instrument is square with AB.

By carefully examining the scale it will be observed (see Fig. 1) that the divisions are not equal, but that they gradually increase from zero upward; herein consists the improvement of this instrument over the ordinary hatchet planimeter invented by Knudsen, of Copenhagen, who shows in a pamphlet published by him that

c1 + c2
I = ------------- p [1 - (R / 2p)²]
2

Where I = the area traced out by the pointer in square inches.

c1 = the distance between the dents, X and Y, in inches.

c2 = the distance between the dents, X1 and Y, in inches.

p = the length of the instrument from center of hatchet to point
in inches.

R² = the mean square of the radii of the figure.

The making of such a calculation for every area measured is, of course, quite out of the question. The labor involved would be as great as calculating the area by the ordinate or by Simpson's method; hence it is usual to neglect that part of the formula inclosed within the square brackets, which amounts to assuming the area to be equal to the product of the mean side shift of the hatchet by the length of the instrument; this, however, involves an error too big to be neglected, and, moreover, one that is not a constant fraction of the area measured, thus:

Area of circle, square inches. 10 20 30 40
Error per cent. 0.8 1.6 2.4 3.2

These errors are, however, compensated for in Goodman's improved instrument by making the scale with constantly and regularly increasing divisions. If, however, the area dealt with be not a circle, the error involved in assuming that its R² is equal to the R² of a circle of equal area is so small that it is quite inappreciable on a scale which only reads to one-tenth of a square inch. If the R² for any given area were say 5 per cent. greater than that of the equivalent circle, the error involved would be 0.0016 of the whole quantity when measuring an area of 40 square niches, or 0.064 square inch, a quantity which cannot be measured on the scale. It has been proposed to use a roller and vernier to enable the readings between the dents to be measured with a greater degree of accuracy, but it will be readily seen that the instrument is not reliable to the second place of decimals, hence such refinements are only imaginary. Even with this special scale that we have described above, the inventor does not profess to get as good results as with an Amsler planimeter; he regards his instrument as equivalent to a foot rule in comparison with a micrometric gage as representing Amsler's instrument; but for a great number of purposes the foot rule is sufficiently accurate, and only when great accuracy is required will a micrometer be used, so with the two forms of planimeter. The rougher instrument has some advantages, however; there are no delicate moving parts to get out of order, and the cost is but one-fourth.

In order to ascertain the relative accuracy of various methods of measuring areas, Prof. Goodman has had a large number of irregular areas measured by his first year students within a week or so of their entering the department, before they have attained to any degree of skill in using instruments. The results were as follows. Amsler's planimeter was taken as the standard, the area measured by it being independently checked by an assistant.

Measurement of Areas
Method. Reduced to 100.
Amsler planimeter 100
Goodman " 100 + or - 0.6
Simpson's rule 100 + or - 1.0
Mean ordinates 100 + or - 2.4
Cutting out in cardboard and weighing
against piece of known area 100 + or - 4.4
Equalizing curved edges by drawing
straight lines along boundary
and calculating by triangles 100 + or - 7.0

In the averaging instrument for getting mean heights of figures, the length of the instrument between the hatchet and the pointer is variable. The length is set to the length of the diagram (see Fig. 2); it is then used in precisely the same manner as the planimeter described above. From what we have already said, our diagram in Fig. 5 will be perfectly clear. The mean distance between the dents is in this case the mean height of the diagram, measured on an ordinary scale, or the mean pressure in the case of an indicator diagram measured on a scale to suit the indicator spring.

Knudsen's formula given above applies equally well to this averaging instrument. Neglecting for the moment the quantity in the square brackets, we have I = c p where c = (c1 + c2)/2 but we also have I = h l where h is the mean height and l the length of the figure, therefore h l = c p; but in this instrument we make p = l. Hence h = c, or the mean height of the figure is equal to the mean distance between the dents. The quantity in the brackets is too great to be neglected, however. If we were always dealing with circles, the ratio (R/2p)² would be a constant, and numerically equal to 1/16 or 6.25 per cent. Then all we should have to do would be to use a scale 6.25 per cent. longer than the true scale. But with a long narrow figure such as an indicator diagram, this ratio is much smaller. The measurement of a large number of diagrams gave a mean value of 1/60 for diagrams 4 in. long. It is obvious that, if a diagram be shortened, this ratio will increase, for the value of R does not decrease as rapidly as p, and vice versa; hence this ratio varies approximately inversely as the length of the diagram. Taking the value of 1/60 for the 4 in. diagram, this is equivalent to saying that there is an error of 1 in 60, or 1.67 per cent., in the result, and from the formula it will be seen that the result is too great by this amount; hence, if we make the length, l, between the legs of the instrument 1.67 per cent. of 4 in., or 0.067 in. less than the length from the tracing point to the center of the hatchet, p, we shall compensate for the error on a diagram 4 in. long. But the ratio of this constant quantity 0.067 in. to the length of the diagram also varies inversely as the length in just the same manner as the ratio R/2p, hence this method of correcting the instrument is approximately right for all lengths of diagrams. It must be remembered that if this correction were entirely neglected, it would not exceed two per cent.; hence any inaccuracy in this correction is an exceedingly small quantity, well under 1 per cent.

Whenever errors have been attributed to the instrument, on examination it has always been found that they were due to carelessness in setting the length to the diagram, or to the tracing leg having been grasped so tightly as to cause side slip.

The accuracy of the instrument may be easily demonstrated by drawing a rectangle, say about 4 in. long and 2 in. high, and finding the mean height by the averager, then by doubling the paper over and comparing its height with the mean distance between the dents, it will be found that they agree if the instrument has been carefully used.

In many quarters we know that there is a great deal of prejudice against instruments of this kind. We are quite sure, however, that if only draughtsmen and others would spend half an hour in trying them over, they would save themselves many hours of tedious labor in calculating areas by methods which are seldom as accurate as the results obtained by a planimeter in the same number of minutes.

* * * * *

APPARATUS FOR THE MANUFACTURE OF ACETYLENE GAS.

We give herewith, from Le Genie Civil, illustrations and brief descriptions of some of the more prominent apparatus used for the manufacture of acetylene gas.

Trouvé Apparatus (Fig. 1).--The principle of the gas generator is that of the hydrogen briquet already applied by Mr. Trouvé in his portable lamp. It consists of two vessels, one entering the other. The internal vessel is provided at the bottom with a discharge pipe communicating, through a cock, with the gasometer. It carries a suspended open work basket containing the carbide of calcium. The bottom of this vessel is provided with an aperture through which it communicates with the external vessel containing the water. The latter is brought to a level in the two vessels and attacks the carbide. The acetylene formed is disengaged and enters the gasometer. At the same time, the excess of pressure forces back the water into the external vessel in suppressing its contact with the carbide. The latter, nevertheless, continues to be attacked slowly through the action of the aqueous vapor. If the cock of the apparatus now be closed, the gas will accumulate in the interior vessel and will soon escape through the aperture in the bottom in raising the column of water. Mr. Trouvé has endeavored to remedy this inconvenience by arranging the pieces of carbide in the basket in distinct layers separated by disks of glass. He has, besides, provided his apparatus with an electric alarm, designed to give warning when the holder is too full or when it is on the point of being empty.

Clauzolles Apparatus (Fig. 2).--This apparatus consists of a gas generator, A, hermetically closed and containing the carbide, of a water reservoir, B, communicating with A through a cock, H, and of a gasometer, D, connected with A by the tube and cock, A. The cock, H, is provided with a lever fixed by its extremity to a chain that follows the motions of the holder. When the latter rises or descends, it causes the cock, H, to close or open.

The receptacle, A, is held by a cover fixed by means of four nuts which are removed when it becomes necessary to renew the carbide. The receptacle is removed and replaced by a duplicate one, after the cock, K, has been closed so as to keep the gas in the gasometer.

Bon Apparatus (Figs. 3 and 4).--The acetylene is produced by the reaction of the water falling in small quantity upon the carbide contained in the gas generator, A. The latter is divided into compartments, F, which, filled with carbide, are reached by the water only successively and progressively. When the carbide of the first compartment is exhausted, the water enters the second, and so on. The dimensions and numbers of these departments vary with the size of the apparatus. Each of them contains from ½ lb. to 4.5 lb. of carbide. The box with compartments, F, is covered by a rectangular holder, H, which enters a flat-bottomed receptacle, E, opened above and filled about two-thirds full of water. The latter serves as a hydraulic joint, and, at the same time, as a refrigerator. The holder, H, carries a lead pipe, G', terminating in a funnel into which falls the water from the reservoir, C, led by the pipe, G. This water flows through the extremity, i, of the pipe, G', into the first compartment. Each of the compartments carries, upon the top of the partition that separates it from the following, an aperture through which the water enters the adjoining compartment as soon as the gas in the preceding compartment has made its exit from the gasometer, and so on until the last in the order of the numbers of the compartments.

The flow of the water through the pipe, G, is regulated automatically by a cock, r', with counterpoise. The holder, in rising, closes this cock and gradually cuts off the entrance of the water. The gas produced, once consumed, the holder descends in opening the cock, and the water begins to flow again.

The disengaged acetylene enters the gasometer, B, through the pipe, D. The extremity of the latter is bent into the form of a swan's neck. The gas is thus forced to bubble up through about 2 in. of water, in which it is cooled and freed from all traces of the ammonia that it may contain. The cock, R, in the pipe, D, is a three-way one. The first opens and the second intercepts communication between the gas generator and the gasometer, while the third puts these two parts of the apparatus in communication with the atmosphere.

The total capacity of the gasometer is so calculated that the acetylene produced by a single one of the compartments, F, may be stored up therein upon its exit from the gasometer through the pipe, K. The acetylene traverses a purifying column, I, filled with pumice stone saturated with a solution of sulphate of copper and surmounted by a thin layer of carbide of calcium. The object of the sulphate of copper is to free the gas from phosphorus and arseniuret of hydrogen. The layer of carbide serves to dry it.

It is well to use salt water for the gasometer, as acetylene is but slightly soluble therein.

Lequeux-Wiesnegg Apparatus (Figs. 5, 6, and 7).--The apparatus represented in Fig. 5 is capable of being used in lecture courses. It consists of a tank, B, and a holder, A, which is provided at the top with a wide aperture closed by a hydraulic plug, F. When the apparatus is at the bottom of its travel and ready to be filled with acetylene, the plug, F, as well as the basket, D, and the bucket, E, are removed. The quantity of carbide necessary to fill the gasometer is introduced into the basket. After care has been taken to put a certain quantity of water into the gutter forming the hydraulic joint of the plug, F, the parts, E, D, F, are introduced into the tube, C, in operating rapidly enough to prevent the loss of gas. The holder immediately rises as a consequence of the production of acetylene. The gas redescends through a tube to the bottom of the tank and rises laterally in a column by serving as a guide to the holder and as a support to the cocks designed to send the gas to the points of utilization. A cock, H, placed at the lower part of the apparatus, permits of clearing the piping in case a condensation of water occurs.

The apparatus represented in Figs. 6 and 7 is continuous. It consists of an apparatus with two holders, that is to say, so arranged as to put the least liquid possible in contact with the gas produced, and to thus prevent absorptions and losses. This gasometer consists of a tank, A, of a movable holder, C, and of a stationary holder, B. The generator, E, is formed of a cylinder, at the bottom of which there is a bucket, F, designed for the reception of the greater part of the lime resulting from the reaction. It is closed by a cover, G, arranged with a simple or multiple joint, according to the precision that it is desired to obtain and that may reach 30 centimeters of water. The figure represents the holder at the bottom of its travel.

Mr. Edward N. Dickerson's Apparatus (Figs. 8 to 13).--Mr. Dickerson, of New York in June, 1895, patented several arrangements permitting of automatically regulating the production of acetylene in measure as it is consumed. In the apparatus represented in Fig. 8 the water is led from a sufficiently high reservoir, A, through the pipe, B, into the gas generator, D, and over the carbide, C, placed upon a grate, O. The acetylene forms when the water reaches the carbide, and its disengagement ceases when the pressure forces the water back. The gas passes through the intermedium of a cock, e, into the pipe, W, provided with a cock, Z, into the automatic regulator, G, and then into the gasometer, P R. Between the regulator, G, and the gasometer, Mr. Dickerson interposes an arrangement consisting of an engine, H, actuating an air pump, K, through the pressure of the gas when it is desired to introduce a mixture of acetylene and air into the gasometer. This arrangement is evidently useless when it is desired to collect the acetylene alone. The gas upon making its exit from the gasometer flows through the pipe, T, to the burners, V.

When the holder, R, is filled, the cord or chain, a, passing over the pulley, b, revolves the sector, c, until the pin, g, meets the counterpoised lever, d, of the stopcock, e. In the return of the chain, the other pin, o, carries the lever back to the position shown in the figure.

The gas generator, D, is provided with a discharge cock, E, and a charging aperture, m.

Figs. 9 to 13 show another of Mr. Dickerson's apparatus that permits of an intermittent automatic distribution either of the water upon the carbide or of the carbide in the water in regulating such distribution through the displacement of the holder of a gasometer that collects the excess of gas necessary for the consumption.

Mr. Dickerson rightly remarks that it is disadvantageous to directly control the distribution of the water upon the carbide by means of the holder of the gasometer. In fact, the water cock may remain open before the holder has moved, and there may thus fall upon the carbide an excess of water, giving rise to a production of acetylene greater than the capacity of the holder warrants.

The object of the Dickerson apparatus is to prevent such overproduction and to furnish water or carbide to the gas generator only as long as the gasometer will have been emptied of the desired quantity of gas.

Fig. 10 shows a modification of the gas generator relative to the introduction of the carbide into the water; but the same letters designate the same parts. We shall describe the operations corresponding to the figures.

1 represents the gasometer; 4, the gas generator; 11, the funnel through which the water is introduced into the generator through the pipe, 13; 12, the pipe that connects the generator with the gasometer; 5, a stopcock with counterpoise that alternately opens and closes the communication between the funnel and the generator; 10, a lever connected with the cock, 5; 2, a chain that moves with the holder and maneuvers the lever, 10.

The plug, 6, of the cock, 5, is provided with two conduits, 7 and 8, at right angles. This plug turns 90 degrees, when it is maneuvered by the chain of the gasometer. In the position shown in Fig. 13 the holder is at the top of its travel, and the counterpoise, 9, of the cock is in the position marked by dotted lines in Fig. 9.

In this case, a charge of water fills the chamber 7 and 8 of the cock. This chamber may be oblong, as shown in Fig. 12, in order to increase its capacity. On the contrary, in the position of the counterpoise, 9, marked in continuous lines in Figs. 9 and 11, the channel, 8, communicates with the pipe, 13; the charge of water of chamber, 7 and 8, has fallen upon the carbides, but another quantity of water has not been able to enter, because the revolution of the cock has cut off all communication between the funnel, 11, and the generator, 4.

The acetylene produced by the reaction of the water upon the carbide raises the gasometer holder, which then actuates the plug, 6, of the cock, 5, and allows a new charge of water to enter the chambers, 7, 8. It is only when the holder descends anew to the position, 1, that the water in the chamber, 7, 8, can fall upon the carbide. The quantity of water that the cock is capable of containing is not sufficient to produce a quantity of gas exceeding the capacity of the gasometer, and, as it is impossible to introduce another quantity of water as long as the gasometer has not been emptied anew, any overproduction of gas is thus rendered impossible.

Fig. 10 applies to the introduction of the carbide into the water. It is necessary in this case that the carbide shall have been previously reduced to powder. The funnel, 11, is then closed by a cover, 21, in order to prevent any accidental escape of the gas. The carbide falls into the generator, the bottom of which is open. The latter enters a tank into which flows a current of water, escaping through the waste pipe, 19, in carrying along the lime formed. The height of the water in the tank is sufficient to furnish the pressure necessary to allow the gas to enter the gasometer through the pipe, 12.

* * * * *

DEVICE FOR THE DISPLAY OF LANTERN SLIDES.

Those who would wish to have a little extra shop window attraction by way of displaying slides for the season now at hand might do worse than resort to something of the following style. The appliance can hold any number of slides, according to the diameter of the wheel portion, but in the diagram herewith it is for holding a dozen. The slides can be changed readily, hence a little time would be expended in making a complete change at least once a day.

The relative portions of the sketch being to scale, particulars as to the making of the revolving wheel need not be entered into, as any mechanic could grasp the whole idea at a glance. The edge of the wheel should, of course, be placed facing the window, and a band on the pulley wheel, A, attached to a clockwork or electric motor would supply all the driving power necessary.

In order to get good illumination on the slides, it will be necessary to have a piece of white cardboard or opal glass, B, hung on the axle, the lower side being the heavier, so that although the wheel revolves, it will remain stationary.

Various devices may be resorted to for hanging the slides on the cross rods, but perhaps the method shown at C will prove as simple as any, and consists of small springs which grip the slide at both sides.

By the judicious arrangement of shielded lights placed at side of reflector, a pretty effect is produced as each slide is gradually brought to view.--The Optical Magic Lantern Journal and Photographic Enlarger.

* * * * *

THE FECULOMETER.