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wick Half-tide basin, several elm clows were placed at the west entrance; these were destroyed by the worms in two years, and were replaced by others made of greenheart; the joints of the plank being tongued with deal, to render them completely water-tight. These clows have now been down about seven years, and, although the deal tongueing has been destroyed by the worms, the greenheart planking remains untouched and perfectly sound.

Many methods of protecting common timber have been tried; Metallic but the only successful ones adduced are-1st, the use of broad- protectors. headed metallic nails driven nearly close to each other into the heads and heels of the gates, but if driven an inch apart, the worm penetrates between them; and, 2dly, steeping the timber in a strong solution of sulphate of copper from the Parys copper mines in Anglesea. Some paddles made of English elm thus prepared had been in use upwards of three years, and, on an examination, were found to be very slightly injured; while the unprepared timber about them was quite destroyed.

The author observes, that the outer gates of the wet basins are most injured by the worm, from the sills being low down, and the change of water every tide assisting the growth of the worm. Those parts of the gates which are alternately wet and dry are more injured by the worm than the parts immersed always in the same depth of water. At the spot where a leak occurs from a bad joint, a defect in the caulking, or other cause, the worm commences its attack; so that the most incessant attention is required. Those basins into which the sewers of the town discharge themselves are comparatively free from the worm, from which it would appear that sulphuretted hydrogen gas acts in some measure as a protection against the attacks of the worm.

"An Account of the actual State of the Works at the Thames Tunnel (June 23, 1840)." By M. I. Brunel, M. Inst. C. E.

Tunnel.

In consequence of local opposition, the works have not advanced Thames much since the month of March, 1840; but, as that has been overcome, and facilities granted by the City, the works will be speedily resumed, and the shaft on the north bank commenced.

The progress of the Tunnel in the last year has been, within one foot, equal to that made in the three preceding years. During those periods collectively, the extent of the Tunnel excavated was 250 ft. 6 in., and during the last year the excavation has been

249 ft. 6 in. This progress has been made in spite of the difficulties caused by the frequent depressions of the bed of the river. These have been so extensive, that in the course of 28 lineal feet of Tunnel, the quantity of ground thrown upon the bed of the river, to make up for the displacement, in the deepest part of the stream, has been ten times that of the excavation, although the space of the excavation itself is completely replaced by the brick structure. On one occasion the ground subsided, in the course of a few minutes, to the extent of 13 feet in depth over an area of 30 feet in diameter, without causing any increased influx of water to the works of the Tunnel. The results now recorded confirm Mr. Brunel in his opinion of the efficiency of his original plan, which is "to press equally against the ground all over the area of the face, whatever may be the nature of the ground through which the excavation is being carried." The sides and top are naturally protected; but the face depends wholly for support upon the poling boards and screws. The displacement of one board by the pressure of the ground might be attended with disastrous consequences; no deviation therefore from the safe plan should be permitted.

The paper is accompanied by a plan, showing the progress made at different periods. It is stated that a full and complete record of all the occurrences which have taken place during the progress has been kept, so as to supply information to enable others to avert many of the difficulties encountered by Mr. Brunel in this bold yet successful undertaking.

Instru

June 30, 1840.

HENRY ROBINSON PALMER, V. P., in the Chair.

Description of an Instrument for describing the Profile of Roads." By Henry Chapman, G. Inst. C. E.

The object of the author in the invention of this instrument was ment for to facilitate the mode of making a preliminary survey for railways describing the profile by a machine of a simple construction, and composed of very few of roads. moving parts. It may be thus briefly described.

A light frame with springs and upon four wheels carries the machinery, to which a rotary movement is communicated from one of the wheels, which is keyed fast upon its axle. A double-threaded screw and a series of wheel-work give motion to a cylinder, upon which a length of paper is coiled; this cylinder revolves, and moves simultaneously in the direction of its axis. A pencil, which moves

parallel to the axis of the cylinder, marks a line upon it, with a velocity varying according to the inclination of the road, and is so arranged, that when the machine is passing along a level, the motion of the pencil will equal that of the cylinder. In ascending inclined planes, it will be retarded, and in descending, it will be accelerated. By these means a rising or falling line will be accurately drawn. This variation in the action of the pencil is accomplished by means of a friction-wheel working against a cone, the different diameters of which regulate and determine the speed. The position of the friction-wheel upon the cone is determined by the change of position of a pendulum vibrating within a case which is filled with a dense fluid, for the purpose of rendering its action more uniform.

The machine will trace a section of a road in lengths of five miles upon each sheet of paper, to a horizontal scale of 20 chains per mile, and to a vertical scale of 200 feet to an inch. That no inconvenience may be felt from the smallness of the scale, the instrument is furnished with scales with sliding verniers, from which memoranda can be made of the distance run, and of the variations above or below the datum line. These memoranda are made upon a strip

of
paper, which is fastened on a table, along which an index travels
at a velocity corresponding with that of the paper on the cylinder;
so that the strip of paper being afterwards laid upon the section, the
points marked may be squared down without using the scales.

When the distance of five miles is passed over, a bell gives notice of the working machinery being disengaged; the section is removed; a fresh sheet of paper is introduced, and, as the pencil maintains its position, the' section will be carried on continuously.

This communication is accompanied by three working drawings, showing, on a large scale, the machine in action, and all the component parts in great detail.

"On the Efflux of Gaseous Fluids under pressure." Hood, F.R.A.S., &c.

By Charles

The theoretical determination of the velocity with which gaseous Eflux of fluids are discharged through tubes and apertures, has frequently gaseous fluids. been investigated by mathematicians; and as the question is one of importance in various branches of practical science, the author examines the several theorems which have been proposed for its elucidation, and compares them with the results obtained by experimental researches.

Dr. Papin, in 1686, appears to have first ascertained the law of efflux to be the same for both elastic and inelastic fluids, and the

majority of the writers on the subject since his time have adopted as the fundamental data of their calculations, the hydrodynamic law of spouting fluids, by which the velocity of discharge is found to be proportional to the square root of the height of the superincumbent column of homogeneous fluid.

The author investigates particularly the methods of calculation proposed by Dr. Gregory, Mr. Davies Gilbert, Mr. Sylvester, Mr. Tredgold, and M. Montgolfier, and points out the differences which exist in their several methods. That of Mr. Sylvester is the only one which differs in any considerable degree from the simple law above stated; and his calculation is based upon the supposition that the respective columns of light and heavy air represent two unequal weights suspended by a cord, hanging over a pulley-by which mode of calculation, in the cases selected by the author for comparison, a result is obtained of only about one-third the amount given by the other methods. These calculations are compared with some experiments made by Sir John Guest at the Dowlais Iron Works, and also of Mr. Dufrenoy at the Clyde and at the Butterly Iron Works, recorded by him in his report to the Director-General of Mines in France. The results are tabulated; giving the pressure of the blast, the area of discharge, the velocity of the blast, the quantity of air ascertained by experiment, and the quantity shown by the several methods of calculation. From all these comparisons the author draws the conclusion that the method of calculation proposed by Montgolfier is the most accurate, as it is also the most simple. If the pressure be ascertained in inches of mercury, it is only necessary to find the column of air in feet equivalent to the pressure, and to multiply this number (as in the common case of gravitating bodies) by sixty-four feet, and then the square root of this product will give the velocity of discharge in feet per second. The equivalent height of the column of air in feet is found by multiplying the number of inches of mercury by 11,230 and dividing the product by 12, mercury being 11,230 times the weight of air. Allowing for a small loss by friction in the quantity found by experiment, the agreement between the theoretical and experimental quantities is extremely near. Rules are likewise given for applying these calculations to other gases of different specific gravities, which are also applicable to chimney draughts and to the expansion of air by heat.

INDEX

TO THE

MINUTES OF PROCEEDINGS.

1840.

A.

Addams, H., elected graduate, 37.

Address of the President to the annual general meeting, 15.

Annual Report, 1.

Arches, on the expansion of, 4.-Experiments to ascertain the effect of tempe-
rature on the arches of Southwark bridge, 4.-Ditto ditto at Staines
bridge, 5.

Autogenous uniting of lead and other metals, 27.

Azimuth cap as an addition to the common level, 31.

Bateman, J. F., elected member, 83.

Batson, R., elected graduate, 28.

B.

Bazalgette, J. W., on reclaiming land from the sea; with plans illustrative of
works in Loughs Swilly and Foyle, 41.

Birch, J. B., elected graduate, 41.

Boilers, description of an apparatus for preventing the explosion of steam, 55.
Botfield, B., elected associate, 54.

Bourns, C., on setting out railway curves, 56.

Bridge, Southwark, experiments to ascertain the effect of temperature on the
arches of, 4.

Staines, ditto ditto, 5.

suspension, proposed for Haslar Lake at Portsmouth, 52.

Browne's hydraulic level, on, 20.

Bruff, P., elected associate, 61.

Brunel, M. I., on a mode of dowelling timber, 6.—An account of the actual
state of the works at the Thames Tunnel, June 23, 1840, 85.

I. K., remarks on the use of American white cedar wood for covering
locomotive boilers, 45.

Budd, T., elected graduate, 33.

Burke, J. St. G., elected associate, 54.

Burn, A., account of a proposed suspension bridge over the Haslar Lake at
Portsmouth, 52.-Dimensions of the principal parts, 53.

Bury, E., account of the performances of the locomotive engines on the London
and Birmingham Railway during the year 1839, 33.-Remarks on American
locomotive engines, 48, 49.

Bye-laws, remarks on the alteration of the, 2.

[1840.]

b

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