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collected, at immense pains, the prices of materials and of labour as paid in the erection of Westminster Bridge; he has also compiled a journal of works from the commencement of the undertaking to the time the bridge was opened. These most interesting and instructive documents are collected from the voluminous records deposited in the Bridge Office.

The paper is accompanied by an atlas of eleven drawings, shewing the site and all the details of the bridge, with fac-simile signatures of Charles Labelye the engineer, and Messrs. Jelfe and Tufnell the contractors.

May 29, 1838.

The PRESIDENT in the Chair.

James Routh and B. Townshend were elected Graduates; and F. Braithwaite, J. Milner, N. King, J. Richards, P. Henderson, were elected Associates.

Decompo

sition of Water.

The minutes of the conversation on the explosion of Steam Boilers were read, and Mr. Lowe stated that the ordinary process of making water gas shewed that an iron plate would readily decompose steam or water. The decomposition of water goes on extremely well until the oxidation of the tube has advanced to at least 3 ths of an inch. An iron tube begins to make gas extremely fast at first, and continues until the tube is cased with a thick crust of protoxide of iron.

16

Thames

Tunnel.

The drawings of the Shield at the Tunnel were exhibited, and Mr. Brunel explained the construction of the Shield, and the manner in which it is advanced and worked.

June 12, 1838.

The PRESIDENT in the Chair.

Captain Robe, R.E. and James Thomson, were elected Associates.

Staff.

Mr. Bruff exhibited an improved form of Levelling Staff. Improved The figures on this staff are inverted, so that when viewed by an Levelling inverting telescope in the usual manner, they appear erect, and are read off without any danger of mistake; which may readily occur when some figures, as for instance 6 and 9, are read off inverted. The mechanical arrangements for extending it are with the view of securing greater steadiness. The principal improvement consists in there being attached to the bottom an universal joint, fixed to an iron plate; this plate remaining fixed, the necessary errors consequent on moving the staff for reversing its face, when the last forward station is to become the next back, are avoided.

It was suggested that the universal joint would be attended with great advantages in sloping ground; in general, however, the tripod invented by Mr. Simms was sufficiently convenient.

Mr. Bald suggested that the universal joint would be extremely serviceable if placed on something solid. It was his practice to drive a wooden plug into the ground, on which the staff was set; these plugs were left in, and serviceable for verifying the observations. He had levelled through a distance of forty miles, leaving a plug at every station.

"Description and Drawing of the Ice Boat. By S. Ballard, Ice Boat. A. Inst. C. E."

The principle of breaking ice adopted by Mr. Ballard, as explained in a communication made last Session,* consists in forcing the ice upwards instead of forcing through it horizontally, or by pressing it down. For this purpose a frame, coated with sheet iron, is laid over the front of a boat, with an inclination downward from the boat, the lower end being under the ice. The paper describes the construction of the boat by reference to a detailed drawing and section.

* See Minutes of Proceedings, Jan. 31, 1837.

Flow of

Water through Pipes.

66

Experiments on the Flow of Water through pipes of different lengths. By W. A. Provis, M. Inst. C. E."

In this paper are recorded two hundred and eight experiments on the flow of water through leaden pipes of 1 inch diameter, of lengths 100, 80, 60, and 40 feet, and for heads of water of 35, 30, 24, 18, 12, and 6 inches. The arrangement of the experiments is described with great accuracy, and the results of the experiments are given in twelve tables, shewing the length and inclination of the pipe, the head of water at the upper end of the pipe, the time from turning the water into the upper end of the pipe to its reaching the lower end, the time of filling the receiver, the discharge in cubic feet per minute, and the mean discharge per minute. To each set of experiments is appended a column of remarks, in which the state of the pipe as to dryness, and the quantity of water in the discharging end, are recorded; these circumstances having considerable influence on the quantity of the discharge.

The experiments are tabulated in a different form, shewing the effect of a given head of water in pipes of different lengths and inclinations. The following important results are deduced. In level pipes the quantity of water discharged is nearly in the inverse ratio of the square root of the length; but the departure from this rule is greatest in the shortest lengths and greatest heads. In inclined pipes, the increased discharge is greater in the long than in the short pipes. The increased discharge for an increased head is nearly in the same proportion through the long and short lengths.

June 19, 1838.

The PRESIDENT in the Chair.

"Table of Gradients. By C. Bourns, A. Inst. C. E."

Gradients.

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Roads

"On the construction of Roads on Deep Bogs and Moss. By W. Bald."

In this paper the author gives a detailed account of the construcover Bogs. tion of Roads through Bogs, and of the methods of securing the foundations of small bridges in boggy places; also some suggestions on the formation of Railways on deep Moss.

The general principles are as follow. The first operation after laying out the line of road is to drain thoroughly the bog over which it is to pass. For this purpose main drains and counter drains parallel to the line of road are to be cut with a regular discharging fall along the bottom. Transverse drains must also be cut betwixt the main and the counter drains, so as effectually to drain off all the surface water and stagnant pools. The cutting of these drains must be carried on gradually, and by degrees; if the bog be moist, the operations, which can only be carried on at dry seasons of the year, will probably have to be continued over three or four years before the drains become permanently fixed at the required dimensions. The counter drains are essential, as they relieve the pressure on the sides of the main drain, and consequently prevent it filling up. The bog stuff cut out is to be dried, and when the bog under the line of road has become sufficiently dry, the road is to be levelled, and made of proper shape, and the cross drains are to be filled with dry turf.

The road-way is then to be floored or trunked over with five courses of dry heathy sods, which are to be well rolled with a heavy cylinder. Upon this trunking is to be laid a soling, consisting of a mixed mass of prepared earth and gravel, of about six inches in thickness, and the whole to be coated with good clean gravel. The road metal is then to be laid on, in two successive coats, each of about three inches in thickness, the first being well consolidated before the second is laid on.

The great points to be aimed at are perfect drainage and good trunking, as, if these are not attained, roads constructed on bog will lose their shape, become ruinous, and soon go to decay.

Size of The author considers the form and size of hammers employed in hammers. breaking hard stones.

Turf Fuel.

These are frequently too heavy; a hammer weighing about a pound and a quarter, of an elliptical form, pointed at the ends, the area of end being about th part of a square inch, appears to be best suited for ordinary purposes.

The turf of bog, being carbonized, makes excellent fuel, and may be employed in the manufacture of iron, and such iron is extremely

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