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wheels describe evolute circles, bearing the same proportion to their respective pitch circles, which the evolute circle of the smallest wheel bears to its pitch circle-thus, if in the smallest wheel the evolute circle is less than the pitch circle, let all the other evolutes be less than their pitch circles. From these evolute circles as bases, describe the involute curves of the teeth, making the curves pass through the points set out for the teeth, upon the pitch line.

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"An Account of some Experiments to determine the force necessary to punch holes through plates of wrought iron and copper." By Joseph Colthurst.

These experiments were performed with a cast-iron lever, 11 feet long, multiplying the strain ten times, with a screw adjustment at the head, and a counterpoise.

The sheets of iron and copper which were experimented upon were placed between two perforated steel plates, and the punch, the nipple of which was perfectly flat on the face, being inserted into a hole in the upper plate, was driven through by the pressure of the lever.

The average results of the several experiments (which are given in a detailed tabular form) show that

The power required Inch diam. Through an Inch thick.

Hence it is evident, that the force necessary to punch holes of different diameters through metals of various thicknesses, is directly as the diameter of the holes and the thickness of the metals. A simple rule for determining the force required for punching, may be thus deduced.

Taking one inch diameter, and one inch in thickness, as the units of calculation, it is shewn that 150,000 is the constant number for wrought-iron plates, and 96,000 for copper plates.

Multiply the constant number by the given diameter in inches, and by the thickness in inches; the product is the pressure in pounds, which will be required to punch a hole of a given diameter, through a plate of a given thickness.

It was observed that, duration of pressure lessened considerably the ultimate force necessary to punch through metal, and that the use of oil on the punch reduced the pressure about eight per cent.

A drawing of the experimental lever and apparatus accompanied the communication.

Mr. Sopwith called the attention of the meeting to the valuable Geological Sections presented by the railway cuttings, and other engineering works now in progress; this was particularly the case on the North Midland Railway, where the crops of the various seams of coal, with the interposing strata, were displayed in the clearest manner, developing the geological structure of the country which the railway traverses. Numerous similar instances induced the British Association to devote a sum of £200. (which it was believed would be increased from other sources), for obtaining authentic records of such sections, before the action of the atmosphere or the progress of vegetation should have obliterated the instructive pages of geology, which the engineer had opened to view.

The Committee of the British Association, especially charged with this subject, were desirous of bringing it before the Institution of Civil Engineers, for the double purpose of receiving from its Members those suggestions which they are so competent to give, and of obtaining from them that powerful aid and cooperation which the practical nature of their engagements so essentially enabled them to afford; it was accordingly suggested that the Council should receive from Graduates, descriptive papers and measured delineations of sections, as their communications previously to their Election. Much assistance might thus be

rendered, and the contributions, after having been read at the Institution, might be added to the general series preserved in the Museum of Economic Geology, which under its present able direction, is becoming daily more interesting both to the engineer and the geologist.

Mr. Sopwith exhibited a specimen of a blank chart, prepared by Mr. Phillips, of York, for the committee. It consisted of a sheet engraved in squares, on a scale of forty feet to an inch, containing a space equivalent to 800 feet in length, and 600 feet in height, upon which it was proposed to delineate their sections, in their true vertical and horizontal proportions; the base line representing either the level of the sea at half tide, or the datum line of railway, as might be most convenient. There would remain in every case a large portion of the sheet unoccupied by the section, and upon this it was proposed to exhibit, on a magnified scale, the details of the section; the fossils and other organic remains might also be shown, as the divisions of the squares would enable the sketches to be made of any dimensions in correct proportions. An example of these charts had been prepared by Mr. Phillips, giving a section of a deep cutting on a railway, the enlarged portion exhibiting the details of the strata at two particularly interesting points, as also of the specimens of sigillaria, stigmaria, &c., in that formation.

Mr. Sopwith, also laid before the meeting a set of models, which were intended as hand specimens for the purpose of familiarly explaining faults, slips, or dislocations of the strata, and other geological phenomena, which could not be clearly demonstrated without such assistance. One of these models represented the horizontal deposition of stratified rocks, and the subsequent removal or degradation of such rocks, forming valleys of denudation. Another, by the displacement of the lower rocks, exhibited the formation of a slip dyke, or fault, which was the "lode or vein" of the mineral miner, and the fault" or 66 trouble" of the collier, as these interruptions of the continuity of the bed of coal were generally termed. Another model showed a succession of slip dykes disturbing the stratification, so as to present the

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appearance of a great abundance of coal at the surface by the cropping out" or "bassetting" of a number of seams or beds of coal, whereas in reality there was only a repetition of the same beds. By examining the base of the model, and also by opening it on an oblique plane nearly parallel with, and at a short distance below, the surface, it would be found that there was no coal at all. A fourth model exhibited the conditions under which some of the largest collieries in the kingdom are worked, namely, that the seams of coal do not appear on the surface, but on opening the model a vertical section is exhibited, and the several beds are shown, disturbed as in the former case by faults or dislocations, but which have not the effect of bringing the coal to the surface.

It has always been difficult to demonstrate, without the aid of models, the apparent form of strata, as effected by the contour of the country; sometimes the rocks form a V, pointing up the valley, and sometimes in the opposite direction. General observers, and even practical miners, were apt to conclude, that this different direction of the point of the V, indicated a different direction of the strata, but the models showed that in both cases the direction of the strata was the same; that in both cases the rocks were inclined in the same direction as the valley, the only difference being, that in one case the rocks form a greater, and in the other a less angle with the horizon than the bottom of the valley. The other models exhibted the "up-cast" and " downcast" which occur in coal mining, and intersections of veins of different ages, &c. &c. Most of the specimens shown, presented details of the carboniferous formation, but models of this description were of course applicable to every formation and to every kind of geological structure. Mr. Sopwith brought forward this subject in hopes that eventually a close union and active cooperation might be established between the leading scientific institutions of this country, and more especially that the Geological Society and the Institution of Civil Engineers would unite in promoting the progress and improvement of geology and engineering.

Original Communication.

ON THE ENGINEERING OF THE ANCIENT

EGYPTIANS.

BY J. S. PERRING, ESQ.

No. II.

Our last paper contained some remarks upon the hydraulic engineering of the Egyptians, and we propose continuing the same subject,-in describing the mode by which the Fyoom was supplied with water, and converted from an arid plain, surrounded by desert mountains, to the most fertile district of the richest country in the world.

Our old friend Herodotus does not seem to have described these works with his usual fidelity; but, by magnifying their extent and purpose, has given his narrative somewhat of the marvellous. We shall not, therefore, on this occasion, transcribe his account, but confine ourselves to a description of the works, as they appear to have been; derived from an examination of their remains, during the autumn of 1839.

The canals, which conveyed the waters from the Nile to the districts, and into the lake, are of great magnitude; but Herodotus, and other authors, have confounded them with the celebrated lake Moris, which is only artificial, so far that the tract of low ground which it covers, was formed into a lake by being made the receptacle for the superfluous waters of the annual inundation of the Nile.

The canals were excavated for the double purpose of supplying the plains of the Fyoom with water, and as a means of drawing off a portion of the waters of the inundation, when its increase was too great, and the country endangered in consequence.

Though the Fyoom is connected, by a strip of land, with the valley of the Nile, yet it is impossible, from the height to which the rock rises in the gorge, that the waters of the river could naturally have connection therewith.

Without water the laughing plains of the Fyoom would be an arid desert; but its capabilities do not appear to have been long neglected; as far as the accounts which have reached us, we may