ther a level line agrees with low water, mean water, or high water, and thus what is the true level of the sea.

A paper was then read, by Mr. Lubbock, on the importance of forming new empirical tables for finding the moon's place.

Mr. Phillips next proceeded to offer a brief statement of the means taken by the committee of the Association for the purpose of procuring regular and uniform experiments on subterranean temperature. The errors incidental to observations made in the air or water of mines had induced the committee to recommend observers to attend simply to the temperature of the rocks themselves; with this view thirty-six thermometers had been duly compared, and the errors of them ascertained. The results confirm the alleged increase of temperature beneath the surface. In one instance the instrument stood at seventy-eight degrees constantly, whilst the mean temperature of the air above was forty-seven degrees.

Mr. Craig read a paper on Polarization, with a view to shew that the phenomena are referable to the division, and consequently to the weakening, of the impulse of light; and the inability, therefore, to pass through other regular structures without exhibiting phenomena which arise out of the peculiarities of such structures.

TUESDAY, Professor Whewell having taken the chair, Mr. Russell proceeded to read his paper on the practical applications of certain principles of hydrodynamics, which had been developed in the course of a series of experimental researches, in which he had been engaged for several years.

The investigations of Mr. Russell led to important results; and the present paper regards principles which open a wide field for the improvement of the construction and transport on canals, and of the navigation of shallow rivers.

The increased resistance of a fluid to a solid moving upon its surface, is well known, and has been supposed to follow the Newtonian law. This is sometimes true, although very rarely. It is scarcely ever true of a vessel moving in shallow water. For example, these are resistances, measured in pounds weight, required to move the same vessel at different velocities.

These apparent inconsistencies had been reconciled with theory by the discovery of a very beautiful phenomenon forming a most important element of the resistance. The law, connecting the resistance with the velocity of the propogation of waves in the fluid, gave to these results of experiment, unity and consistency. It had been ob

served that the motion of a vessel through a fluid communicates to its particles motion in the form of waves. These waves are formed by the anterior accumulation of the fluid which the vessel pushes before it; they propagate themselves in the same direction with the motion of the vessel, and with a velocity nearly uniform. Their form is determinate; their length nearly constant, and their velocity nearly uniform. From the formation of these waves, the resistance is very different from the amount on the supposition of quiescence in the fluid.

The velocity of the wave is that acquired by falling through a space equal to half the depth of the fluid. In water about four inches deep, the velocity of the water is about three feet a second; in a depth of seven inches, the velocity is about four feet a second; at a depth of thirteen inches, the velocity of the wave is five feet a second; at forty inches, ten feet a second; and at sixty-six inches, more than eight miles an hour.

The resistance of the fluid was found, by a long train of experiments, to be intimately connected with the formation of the waves, in such a manner that the resistance was greater than in the ratio of the squares of the velocities, or less than in that ratio, according as the velocity of the wave was greater or less than that of the vessel. It was thus found that the generation of waves at the prow of the vessel impeded its velocity, so long as its motion was less rapid than that of the wave; when, on the other hand, a sufficient power was obtained to make the vessel move faster than the waves, the heaping up of water at the prow ceased, the waves fell back towards the middle of the vessel, and, bearing it up upon their summits, carried it on with diminished immersion and resistance. From the law of the wave the following practical conclusions are to be drawn. 1. That in every canal there are two most serviceable rates; one below the wave, up to about two-thirds of its velocity, and another immediately beyond the velocity of the wave. 2. That all velocities a little slower than that of the wave, are in some cases impossible, in others impracticable, and in all unprofitable. 3. That in shallow rivers and canals depth is an element of much greater importance than breadth. 4. That banks nearly vertical are, for all velocities, more economical of power, and more durable, then wide surfaces and long slopes. 5. That very high velocities are to be attained in shallow water with greater economy of power, by getting over the wave.

Professor Powell read Observations for determining the Refrac tive Indices for the Standard Rays of the Polar Spectrum in various Media; a subject to which he has for years directed his attention.

Sir David Brewster read a paper on a singular development of polarising structure in the crystalline lens of the eyes of animals, after death. The inquiries which form the subject of this paper were made by comparing the changes which take place in the polarising structure of the crystalline lenses of animals in old age with those

after death, the lenses being placed in distilled water, as being the only fluid which did not affect the transparency of the cepsili. From these investigations Sir D. Brewster has been led to conclude that there is in the crystalline lens a capability of being developed by the absorption of the aqueous humour, that a perfect structure is not produced until the animal frame is completely formed, and that when it begins to decay the lens changes its density and focal length, and sometimes degenerates into that state called hard and soft cataract. Sir D. Brewster is led to entertain a hope that these researches may furnish a means of preventing or curing this alarming disease. 11. W di

The Rev. Mr. M Gauley having been called on by the president to read a paper in continuation of the one which he gave last year, respecting the theory of the Application of Electro-Magnetism to Mechanical Purposes, commenced by stating that he had met with many practical difficulties, as might be expected, in preparing for the section a small model of a machine, intended to act with effective power; one of the most serious of these was, that the crank and fly-wheel could not be made to move along with the primary moving pendulum. He then proceeded to give his views of the theory of electro-magnetic influence, and the best modes of constructing the several parts of the apparatus, so as to produce the greatest effect, and illustrated the subject by copious extracts from a most laborious course of experiments, which it would appear that the reverend gentleman had himself instituted and conducted.

At the termination of the reading of this paper, which extended to great length, Professor Ritchie made some observations on its want of novelty; and stated that every part of the theory, and all the experiments had appeared in several of the most widely circulated scientific journals.*

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WEDNESDAY.The business was commenced by Mr. Harris, "On some Phenomena of Electrical Repulsion."

Professor Challis's Supplementary Report on the Mathematical Theory of Fluids gave an account of the application of mathematics to problems in the equilibrium and motion of fluids, which had not been touched upon in the author's previous reports. These were principally the mathematical theory of elastic fluids, as bearing on the determination of the heights of mountains by the barome ter, the amount of astronomical refraction, and the theory of the the determination of the velocity of sound as affected by the de velopment of heat. The bases on which these theories rest were stated, and a comparison made of the theoretical results with experiments.Pamon... :

Mr. Adams made a communication on the Interference of Sound. He made some pleasing experiments with a tuning fork and a small glass tube, one end of which was closed. When the fork was held

Mr. M'Gauley has published a letter in The Athenæum, complaining of this bitter and unfounded attack on his theory after he had quitted the room.

VOL. V.-NO. XVII.

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over the latter, the column of air within produced a sound, which increased or diminished according to the distance between them. With two tubes, one placed horizontally, the other perpendicularly, a curious phenomenon was observed: when the tuning fork was put in vibration in a certain position between the two unclosed ends of the tubes, no effect was observed; but when this position was changed, or the mouth of one of the tubes closed, a very audible sound was produced. With a tube of fourteen inches long, open at either end, tones were only obtained by stopping a small hole in the centre; but on inserting into this a glass tube of three inches in length, the effect was reversed, the sound being only heard when the glass was unclosed upon increasing this small tube to seven inches, being half the lengh of the larger one, no sound was produced. Mr. Adams said he would not attempt to explain the cause of these phenomena, but leave it to Professor Wheatstone and other abler hands.

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THURSDAY.-Mr. Peacock read a communication from Mr. Talbot on the Integral Calculus.

Dr. Apjohn then read a paper on the use of the Wet-bulb Thermometer in determining the specific heat of Air.

The Rev. Mr. Scoresby gave an account of two very delicate magnetic instruments. The first of these he called a magnetimeter, from its extreme delicacy in detecting and measuring exceedingly minute magnetic influences. The second instrument was a very powerful, yet very light, magnet, mounted in such a manner as to be eminently fitted for observing accurately the variation of the needle, as well as its diurnal and annual changes.

Professor Forbes, in a communication on the Terrestrial Magnetic Intensity at various heights, has gone far to determine an important but disputed question in Physics, viz. the change in magnetic intensity at different altitudes above the earth's surface. He stated, briefly, the results of forty-five series of observations with Causteen's intensity needles at 13 stations in the Alps and Pyrenees, from six to one thousand feet above the level of the sea, and compared with the intensities observed in the intermediate valleys. The general result at which he arrives is, that there is no general decisive indication of diminished intensity with height, at least within the limits of error of the instrument, and certainly, if it exists, the diminution must be considerably smaller than M. Kuppfer has supposed.

A paper, by Sir D. Brewster on the action or christallyzed surfaces, was read, and gave rise to some discussion on the part of Sir W. Hamilton and Mr. M'Culloch, but the statements of the paper do not admit of abridgment.

Dr. C. Williams gave an account of an improved ear-trumpet, by which sounds are rendered audible at three times the usual distance.

Evening Sitting.-Mr. G. Hall read a paper on the Connection of the Weather with the Tide, and observed that the barometer undulates at the changes of the moon, but more commonly sinks than

riscs; the weather is then generally unsettled, with high winds; as the weather settles, it not unfrequently remains in an indeterminate state. These variations apply to all the changes of the moon.

Mr. Ettrick read three papers; the first on an instrument for observing Terrestrial Magnetism-on improved Rubbers for Electrical Machines and on a new Instrument for trying the Effect of Electrical Discharges in Rarefied Air, or in different kinds of Gases.

Mr. Adams, in a paper on the vibration of bells, endeavoured to explain a peculiar beat frequently heard in the sound of a clock or tower bell, which he considers to arise from unequal thickness of the metal; this he illustrated by some striking experiments on a glass bell. An interesting conversation then took place, in which Professor Stevelly, Professor Forbes, and Mr. Adams took part.

FRIDAY. The papers read this day were by Mr. Whewell, on a new Anomometer. In this communication Mr. W. explained a method of tracing or registering the course of the winds through a given period by the motion of a pencil, on an appropriate scale, so as to obtain eventually a true type of the winds, which has never yet been arrived at by other instruments.

Sir D. Brewster read a paper describing a contrivance by which he was enabled to render distinct the dark lines of the spectrum under the most unfavourable circumstances, and obtain other useful effects. The method was to introduce a cylindrical refractor between the eye and the eye-glass of the telescope, the effect being, as he shewed, to give a linear form to most irregular images.

Dr. Hare explained many interesting phenomena attendant on the electric spark and the divergence of electrified bodies.

Mr. Hodgkinson read an Account of some Experiments, at the request of the Association, to determine the comparative strength and other properties of Iron, made with the hot and cold blast, at the Carron, Devon, and Buffrey Works, under similar circumstances; the former he considered somewhat weaker, and its specific gravity somewhat less, except at the Devon Works.

SECTION B.-CHEMISTRY AND MINERALOGY.

President-Rev. Professor Cumming.
Vice-Presidents-Dr. Dalton, Dr. Henry.

Secretaries-Dr. Apjohn, Dr. C. Henry, W. Herapath, Esq.

Committee-Dr. Barker, Professor Daubeny, Rev. W. Vernon Harcourt, Professor Hare, Professor Johnston, Professor Miller, Richard Phillips, Esq., Drs. Roget, Turner, R. Thomson, T. Thompson, and Yellowley; W. West, C. Coathupe, G. Lowe, H. Watson, Esqrs., Col. Yorke, Rev. W. Whewell.

MONDAY.-The first paper read was on the Phosphate of Soda, and consisted merely of chemical details.

Mr. Ettrick produced and explained an improved blow-pipe, and Mr. Hare, of Philadelphia, a somewhat similar apparatus.

Mr. W. Herapath gave an Analysis of the Bath Waters, and fur