property of giving a wider field of distinct vision than the common ones. The lenses used for this purpose are meniscuses, in which the convexity predominates for long-sighted persons, and concavo-convex lenses, in which the concavity predominates, for short-sighted persons. Convex lenses possess peculiar advantages for concentrating the sun's rays, and for conveying to an immense distance a condensed and parallel beam of light.

M. Buffon found that a convex lens, with a long focal length was preferable to one of a short focal length, for fusing metals by the concentration of the sun's rays. A lens, for example, 32 inches in diameter, and six inches in focal length, with the diameter of its focus eight lines, melted copper in less than a minute; while R small lens, 32 lines in diameter, with a focal length of six lines, and its focus two-thirds of a line, was scarcely capable of heating copper. The most per. feet burning lens ever constructed, was executed by Mr. Parker, of Fleet-street, at an expense of TMU. It was made of flint-glass, was three feet in diameter, and weighed 212 pounds. It was inches thick at the centre; the focal distance was six feet eight inches, and the diameter of the sun in its focus one inch. The rays refracted by the lens were received on a second lens, in whose focus the objects to be fused were placed. This second lens had an exposed diameter of 13 inches; its central thickness was lj$ of an inch; the length of its focus was 2!) inches. The diameter of the focal image was threeeighths of an inch. Its weight was 21 pounds. The combined focal length of the two lenses was five feet three inches, and the diameter of the focal image half an inch. By means of this powerful lens, platina, gold, silver, copper, tin, flint, quartz, agate, &c, were melted in a few seconds. Various causes have prevented opticians from constructing burning lenses of greater magnitude than that made by Mr. Parker. The impossibility of procuring pure flint glass tolerably free of veins and impurities for a large solid lens; the trouble and expense of casting it into a lenticular form without flaws and impurities; the great increase of central thickness, which becomes necessary by increasing the diameter of the lens ; the enormous obstruction that is thus opposed to the transmission of the solar rays, and the increased aberration which dissipates the rays at the focal point, are insuperable obstacles to the construction of solid lenses of any considerable size. In order to improve a solid lens formed of one piece of

tween a b and the left-hand surface of o X. A lens thus constructed, would be incomparably superior to the solid one, *»cr xOAj'but such a process would be impracticable on a large scale, from the extreme difficulty of polishing the surfaces A n, c r, nb,T a, and the left-hand surface of N o j and even if it were practicalble, the greatest imperfections in the glass might happen to occur in the parts which are left.

In order to remove these imperfections, and to construct lenses of any size, Dr. Brewster proposed, in I 111 1, to build them up of separate zones, each of which was again to be composed of separate segments, as shown in fig. 2. This lens is composed of one central lens, Abcd, corresponding with its section, N o, in rig. 1, of a middle ring, E F o H, corresponding to B o M E, in fig. I, and consisting of five segments, and another ring, Him, corresponding to A d E r, and consisting of eight segments. The preceding construction obviously puts it in our power to execute these compound lenses of pure flint glass, free from veins; but it gives another great advantage, namely, that of enabling us to correct very nearly, the spherical aberration, by making the foci of each zone coincide. One of these lenses was constructed under Dr. Brewster's direction, for the Commissioners of Northern Lighthouses, by Messrs. W. and P. Gilbert. It was made of pure flint ulass, and three feet in diameter, and consisted of many zones and segments. Lenses of this kind have been made in France of crown glass, and have been introduced into the principal French lighthouses; a purpose to which they are infi

Fio. 2.

L

nitely more adapted than the best constructed parabolic reflectors made of metal. A polyzonal lens of at least four feet in diameter, has been executed as a burning glass

A. D. M.

INSTITUTION OF CIVIL ENGINEERS.

ABSTRACT OF PROCEEDINGS ON RAILWAYS.

Session, 1839.

"On Tubing the Boilers of Locomotive Engines." By George Buck, M. Inst. C.E.

In this communication, the author has attempted to determine the diameter of the tubes of the boiler of a locomotive engine, so that the effect in the generation of steam may be a maximum. '1 he following are the conditions upon which the problem is solved:—That the evaporating effect of the hot air, in passing through the tubes, is in proportion to the extent of surface in contact with the hot air, and as the time of contact conjointly. The following are the results of the investigation :— The distance between the centres of two adjacent tubes should be equal to four times the interval between their internal surfaces—the diameter of each tube should be equal to three times the same interval— that the tubes should be as near each other as possible.

In illustration, Mr. Buck has drawn

two sets of tubes of the locomotive boiler as generally employed, and one as they would be arranged according to the results of this investigation. On comparing the products of the aggregate periphery, and the aggregate area of the tubes, it appears that the boiler, tubed according the above theoretic proportion, is from "21 to 26 per cent, superior to the others.

"Manchester and Leeds Railway Section." By Francis Whishaw, M. Inst. C. E.

This section, prepared under the direction of Mr. Wishaw, is designed to afford a novel and useful method of embodying a great mass of the details required by an engineer when giving evidence before a Parliamentary Committee. This section was constructed before the last Standing Orders, and the author had here anticipated them in putting upon this section much of the detail now required. By sections thus prepared, the engineer can always answer any questions which may be put to him.

"On the comparison between the power of Locomotive Engines and the effectproduced by that power at different Velocities." By Professor Barlow, Hon. M. Inst. C.E.

In this communication the author attempts to lay down an appropriate method for computing the power of locomotive engines; and though, this method will not serve to exhibit the absolute power of the engines, it may serve to exhibit the comparative power under different conditions. We know the number of cubic feet of water evaporated in any given time; the diameter of the driving wheels, the length of stroke, and the capacity of the cylinder; we hence know how many cubic feet of steam have been' employed, and consequently the mean number of cubic feet of steam produced from one cubic foot of water. Again, by experiments that have been made by different writers upon the elastic force of steam, we know the pressure per inch on the piston, and then making due allowance for the resistance oft! e atmosphere on the piston, the friction of the engine gear, &c, there remains the force that ought to be effective on the piston. This being reduced to the circumference of the wheel, should be equal to the resistance opposed by the load, which on a level plane consists of axle friction, road resistance, and the resistance of the atmosphere to the engine and carriages. But this is assuming that the engine has a perfect action, without any waste, which, however much to be desired, can never be the case in practice. Thus, comparing what ought to be done in overcoming resistance with what is done, we shall learn the amount of power wastefully expended.

The author then selects some '■xpcriments from those made on the North Star and Varvey Coombe engines, as reported by Mr. Wood to the Directors of the Great Western Railway, and illustrates by these the proposed method, and exhibits the re suits in tables.

From one of these experiments it appears, that the steam power expended per ton of the gross load amounts to 32lbs., whereas on a tolerably level line it is ge. nerally assumed, that the retardation of such a load does not amount to more than 9lbs. per ton; so that there appears to have been a power expended more than three times as great as the mechanical resistance to which it was opposed, according to views hitherto taken on the subject.

The author then proceeds to consider the resistance to railway trains at different speeds, and these resistances he refers to, 1st. Hint of the atmosphere; 2nd. The friction of the axles; 3rd. The road resistance. He discusses several experiments made by Mr. Wood, and remarks on the great discrepancies which they present— the atmospheric resistance in one case amounting to 353 lbs. and in another to 99.71bs. at the same velocity, viz., 32^ miles per hour; the friction in the former case being 5 or Gibs., and in the latter 20 lbs. per ton. The results of the best experiments on the atmospheric resistance and on friction, show that the former must be considered to vary nearly as the square of the velocity, and the latter to be constant, or independent of the velocity; but this law of the constancy of friction, owing to the peculiar circumstances of the case, cannot hold with respect to the axles of railway trains.

Very much must be attributed to the increase of the road resistance as due to the deflection of the rails at high velocities, and to the state of oscillation to which all the parts of the carriages are subject, and the imperfection of the joints. The author proceeds to make some observations on the actual state of our knowledge with respect to the atmospheric resistance, and the effect of inclined planes on the working of a line of railway. The speed in descending planes is limited by considerations of safety, and in planes of 1-96, 1-100, and 1-220; it is not safe to descend with heavy loads at a greater mean rate than is attainable with the same load on a level; that on planes between 1 -750, and

a level, the whole attainable speed is admissible.

The method of inferring the power of an engine from the quantity of water evaporated, was objected to on the grounds that so much water is lost by priming.

With respect to the resistance due to the imperfection of the joints, it was remarked that engineers are generally so much restricted as to the expense of making the joints of rails, they cannot adopt that which is the best; and it is a question well worthy of attention, whether the best kind of joint is not the most economical, as the wear and tear would be diminished, and the comfort of the passengers increased, by attention to this point.

The experience of the Dublin and Kingstown Railway showed that great advantages would result from a better kind of joint being used. This railway, though so short, and only having been finished about three years, has had, perhaps, more frequent traversings than a longer railway would in fifteen years; the trains started every half hour, and frequently the departures were increased to every quarter of an hour; the opportunities of observing the effect of the carriages upon the rails were, therefore, excellent.

"Description of an instrument for setting out the width of cuttings and embankments of Railways, Canals, or Roads, as particularly applicable to falling or side-lying ground." By Henry Carr, Grad. Inst. C. E.

The object of this instrument is to facilitate the operation of determining the distance of the outer lockspit from the centre line of a cutting or embankment, by avoiding all calculation, and reducing the usual threefold operation into one. The principle of its construction is the formation of a half cross section, which may be easily altered to suit all cases with regard to base, side slope, and inclination of surface. The construction of the instrument is described in great detail by reference to the drawing accompanying the communication. The author states, that he set out a portion of the South Eastern Railway with this instrument, and found it answer exceedingly well. The experience of the first instrument has suggested some improvement in its construction, which is represented in another drawing.

"Observations on the present mode of executing Railways, with suggestions for a more economical, yet equally efficient sys

teio, of both executing and working them." By Francis Wishaw, M. Inst. C.E.

The author at the commencement of this paper, alludes to the principal causes of the threat differences between the original estimate and cost of railways. Among these he enumerates the imperfect knowledge of the strata, which occasions the cuttings and embankments to be formed with slopes, which are dangerous, and add to their cost—the imperfect formation of the embankments, especially in clayey soils, which, in the opinion of the author, ought to be carried up in layers or courses of from 1 k to 2 yards in thickness, sufficient time being allowed for subsidence before the next layer is added—the cost of stations, which in some of the great lines forms a considerable proportion of the whole cost.

The author then proceeds to suggest means for effecting a considerable saving in the original cost of railways, a certain method of preventing accidents by collision, a saving in the annual expenditure, and a better adaptation of the locomotive engine to its work.

With these views he proposes a single line of rails, that the line should be divided with intermediate engine stations, three on the London and Birmingham, for instance, the engines at each being suited to the prevailing gradient of the district. Thus a line of railway may be more easily laid out, as one or two unfavourable inclines will not affect the working of the whole. At each station there must be a small portion of an additional Ge of rails, and also at other convenient intervals. The mode of working such a line is as follows :—Engines are to start simultaneously in each direction from the terminal and intermediate stations. These engines will pass each other at one of the portions of the double line, and the engine being reversed and taking the other train, will return to the station from whence it started, when another exchange of trains takes place. Thus there is a regular interchange of loads throughout the day, and each engine is confined to its own portion of the line, and it is impossible that a collision can take place. Equal accommodation would be afforded to the public, and the engine-man, from being always confined to the same small portion of the line, would be perfectly conversant with every part of it. The saving which would on this system be effected, on the original cost, is estimated at more than 50iW/. per mile.

The attention of the meeting having

been called to M. D. Harcourt's artificial granite for railways, blocks, and other purposes, Mr. Rastrick remarked, that he had about a month ago laid down blocks of the Scotch Asphalte, two feet square, on a portion of the Southampton Railway. The sleeper was put in while the bl> ck was formed. It was usual to bore holes and to fix the chairs by bolts. He had wished to ascertain how far the blocks would stand the driving in of the bolts, without any boring; they bore this without any apparent injury, and he thought these blocks, weighing about 3-J cwt., would answer the purpose better than blocks of other materials.— Railway Times.

THE GALVANIC TELEGRAPH AT THE GREAT WESTERN RAILWAY.

The space occupied by the case containing the machinery (which simply stands upon a table, and can be removed at pleasure to any part of the room) is little more than that required for a gentleman's hat-box. The telegraph is worked by merely pressing small brass keys (similar to those on a keyed bugle) which acting by means of galvanic power, upon various hands placed upon a dial-plate at the other end of the telegraphic line, as far as now opened, point not only to each letter of the alphabet (as each key may be struck or pressed), but the numericals are indicated by the same means, as well as the various points, from a comma to a colon, with notes of admiration and interjection. There is likewise a cross (X) upon the dial, which indicates that when this key is struck, a mistake has been made in some part of the sentence telegraphed, and that an " erasure" is intended. A question— such, for instance, as the following :— '■ How many passengers started from Drayton by the ten o'clock trainh"' and the answer could be transmitted from the terminus to Drayton and back in less than two minutes. This was proved on Saturday.. This mode of communication is only completed as far as the West Drayton station, which is about miles from Paddington. There are wires (as may be imagined) communicating with each end, thus far completed, passing through a hollow iron tube, not more than an inch and a half in diameter, which is fixed about six inches above the ground, running parallel with the railway, and about two or three feet distant from it. It is the intention of the Great Western Railway Company to carry the tube along the line as fast as completion of the rails takes place.

and ultimately throughout the whole distance to Bristol. The machinery and the mode of working it are so exceedingly simple, that a child who could read would, after an hour or two's instruction, be enabled efficiently to transmit and receive information.—Observer.

WRECK OF THE ROYAL GEORGE.

So Much interest has been excited by the recent experiments of Colonel Pasley, that we are induced to give our readers an account, collected from the publ.cations of the day, of the loss of the Royal George, and some subsequent attempts to recover her. It may be proper to explain that the process of careening is performed by removing the guns, or other heavy bodies, to one side of the ship, so that the opposite side rises out of the water. In the summer of 1782, it was found necessary that the Royal George, of 108 guns, commanded by the gallant Admiral Kempenfeldt, and long held as the first ship in the British navy, should receive a sort of slight careen, which the seamen, in their peculiar phraseology, call a parliament heel: the ship having to be laid, in a certain degree, upon her side, while the defects under water, which occasion the examination, are rectified. This seems to be a common operation where the defects are not so great as to require a thorough careen; or where the delay, as in the present instance, of going into dock cannot be allowed; and being usually practiced in still weather and smooth water, is supposed to be attended with so little difficulty or danger, that the admiral, captain, officers, and crew, all continued on board, and neither guns, stores, water, or provisions were removed. This business was undertaken betimes in the u oruing, a gang of carpenters from the Dock attending to assist; and it is said, that finding it necessary to strip off more of her sheathing than was at first expected, their eagerness to come at the leak, induced them to heel her a strake more upon her side than had been intended, and than possibly the commanders knew. The ship, as is usually the case upon coming into port, was crowded with people from the shore; particularly women, who were not estimated at less than 300. Among these were many of the wives and children of the seamen and petty officers, who, knowing the fleet was to sail upon distant perilous service, eagerly embraced the opportunity of coming to see their husbands and fathers. Between eight and nine hundred of the

crew of the Royal George, including marines, were then on board.

In this situation, about ten in the morning, the admiral being writing in his cabin, and much the greater part of the people being then between decks, a sudden and unexpected squall of wind threw the ship fatally upon her side, and her gun-ports being open, and the motion of the cannon probably increasing the violence of the shock, she almost instantly filled with water, and went to the bottom. A victualler which lay alongside the Royal George, was swallowed up in the whirlpool, which the sudden plunge of so vast a body in the water occasioned; and several small craft, though at some moderate distance, were in the most imminent danger.

The admiral, with a number of brave officers, and, in general, most of those who were between decks, perished. The guard, including those who happened to be along with them, on the upper deck, were more fortunate; the greater part being saved by the boats of the fleet. About seventy others were likewise saved. The exact number of people on board at the time could not be ascertained, but it was supposed that from 600 to 1000 were lost. Something about 300, mostly, if not entirely, of the ship's company, were saved. Captain Wairhorne, whose gallantry in the North Sea battle, under Admiral Parker, had procured him the command of the ship, had the fortune, though severely battered and bruised, to be saved; but his son, a lieutenant of the Royal George, happening to be one of those who were unfortunately below, perished.

Such was the fate of the Royal George, which carried the tallest masts, the heaviest metal, and had the greatest number of flags hoisted in her, of any ship in the British navy. She had been repeatedly the seat of command under almost all our great commanders, and upon the greatest occasions during the existing and previous war; and had been peculiarly distinguished under Lord Hawke, in the celebrated battle against M. Couflans, when the French fleet was entirely ruined; and she sunk the Superbe, of 70 guns, by a single broadside, and drove the Soldi Royal, of 84 guns, on shore, where she was burnt. The loss of the ship, notwithstanding the critical period at which it happened, would not however have been much thought of, if it had not been for the brave men who perished so unfortunately in her. Admiral Kempenfeldt, though near seventy years of age, was peculiarly and universally lamented. He was held, both abroad and