interruption of sound produced by a prolonged reverberation, and, comparatively, rarely from a deficiency in the voice of the speaker. The human voice had been heard distinctly at the distance of a mile and upwards in a calm atmosphere. Sir John Ross, Lieutenant Bowen, and many others, had borne testimony to this fact; and in the experiments above alluded to, in the open air, individuals conversed easily at a distance varying from 200 to 1000 feet, when it was calm. In many rooms, in consequence of the repeated reflections between wall and wall, or between roof and floor, the sound of the voice might be heard continued many seconds after the individual trying the experiment had ceased to speak. In a newly fitted-up leaden chamber for the manufactory of oil of vitriol, the sound was heard prolonged for seven seconds; and when the different notes of any chord were sounded successively by any individual, they were afterwards heard blending harmoniously in one compound tone. The leaden chamber was 80 feet long, 15 broad, and 16 high. In numerous public buildings similar effects are observed; but if the walls be made rough and irregular, so as to lose all resilient power, and hung with drapery, the reverberation ceases. On the same principle, the reflecting power of the floor being taken away by a crowded audience, sound is very different in such an apartment from what is observed when it is comparatively empty. The distinction between the actual amount of sound and purity of intonation has not been sufficiently attended to. Much sound may

be produced when the primary impulse is strengthened by combination with the reflected sound of many preceding words, but it has none of that harmony and distinctness which is observed when the primary sound alone is allowed to fall upon the ear. The sound of cannon has been heard at the distance of 300 miles. Captain Stoddart's account of the firing of cannon in the Baltic heard at this distance, affords the most ample and specific information on this subject. The sound of volcanic eruptions has been heard at a distance of nearly 900 miles. It cannot be doubted that the repeated reflection of preceding sounds must interfere most materially with those that succeed; and, from what has been above stated, it is obvious that such reflections must be continued frequently to a great extent in numerous apartments.

In constructing buildings, the following circumstances require to be particularly noticed.

In the most perfect form of building for the communication of sound, any reflected sound must be prevented from continuing so as to interrupt any new tone, by being thrown upon a non-reflecting floor. So long as the reflected sound comes up in time to strengthen the primary impulse before any new sound is heard, it is to be taken advantage of; beyond this it is injurious. A building having low walls, rough and irregular on the surface, an inclined roof terminating in a ridge in the centre, and having any elevation there that might be necessary, the material of which it is made having great reflecting power, with a floor matted and arranged so

so as to absorb all pulses of sound, would be best adapted for this purpose.

All superfluous space should be excluded.

The air should be maintained as uniformly equal as possible.

All concave surfaces ought to be avoided; foci, in such cases, collecting the sound at one point, while in other places it is comparatively deficient.

Dr. Reid, after alluding to the peculiarities in the construction of his class-room, and to many other buildings, adverted to a number of circumstances connected with the roof, walls, and floor of different buildings, the introduction of ornaments, the variety of form that might be adopted according as the walls, roof, &c. were made to reflect or absorb sounds, and the different conditions to be attended to where the speaker was confined to one spot, and where individuals rose in every place to address an assembly.

Experimental Researches into the Laws of the Motion of Floating Bodies. By J. S. RUSSELL.

It was the object of these inquiries to assist in bringing to perfection the theory of Hydrodynamics, and ascertain the causes of certain anomalous facts in the resistance of fluids, so as to reduce them under the dominion of known laws.

The resistance of fluids to the motion of floating vessels is found in practice to differ widely from theory, being, in certain cases, double or triple of what theory gives and in other and higher velocities, much less. These deviations have now been ascertained to follow two simple and very beautiful laws: 1st, A law giving a certain emersion of the body from the fluid as a function of the velocity. 2nd, A law giving the resistance of the fluid as a function of the velocity and magnitude of a wave propagated through the fluid, according to the law of Lagrange. These two laws comprehend the anomalous facts, and lead to the following

Results.

1. That the resistance of a fluid to the motion of a floating body will rapidly increase as the velocity of the body rises towards the velocity of the wave, and will become greatest when they approach nearest to equality.

2. That when the velocity of the body is rendered greater than that due to the wave, the motion of the body is greatly facilitated: it remains poised on the summit of the wave in a position which may be one of stable equilibrium; and this effect is such that at a velocity of 9 miles an hour the resistance is less than at a velocity of 6 miles behind the wave.

3. The velocity of the wave is independent of the breadth of the fluid and varies with the square root of the depth.

4. It is established that there is in every navigable stream a certain velocity at which it will be more easy to ascend the river against the current than to descend with the current. Thus, if the current flow at the rate of one mile an hour in a stream 4 feet deep, it will be easier to ascend with a velocity of 8 miles an hour on the wave than to descend with the same velocity behind the wave.

5. That vessels may be propelled on the summit of waves at the rate of between 20 and 30 miles an hour.

On a Species of Balance and its Application to the Measurement of Electrical Repulsion. By W. SNOW HARRIS.

The principle of this instrument depends on the reactive force imparted to two parallel silk threads without torsion, from which is suspended a horizontal needle or other body. If a needle be suspended by two parallel and vertical filaments of silk without torsion, equally distant from the centre, its position of rest will be horizontal, and in the vertical plane passing through the silk filaments. When the needle is turned through any given angle, the centre of gravity of the mass is raised, so that the needle will, when abandoned to the force of gravity, continue to oscillate, and will be in the state of a body falling down a small circular arc. Mr. Harris has examined the law of this force imparted to the threads, and finds it as the weight and square of the distance between the threads directly and as the length indirectly, and that it is exactly proportionate to the angle of deflection of the needle. Upon these principles Mr. Harris has constructed a balance, which he exhibited to the Section, and by which he can estimate any forces of repulsion in electricity however small. The instrument is not liable to many difficulties which embarrass the use of the torsion balance, and may be employed with advantage in several branches of experimental physics.

On Electrical Attraction. By W. SNOW HARRIS.

The object of this paper was to examine the operation of attraction in electricity, and the laws and differences between the force of attraction actually exerted between two bodies, and the force excited in a neutral uninsulated body, by the influence of a charged body acting upon it at a distance. The author endeavoured to show that the former force varied in an inverse ratio of the distance simply; that the law of the inverse square of the distance, which is the general law for the former force, does not obtain at all distances between bodies, except one of them be uninsulated and neutral; and that in all cases of attraction there are two previous forces to be considered, 1st, the force directly induced in the neutral body; 2nd, the effect of this induced force upon the charged body; which last he called

C

the reflected force, and attempted to prove that the whole attractive force between these bodies varies with these forces conjointly, so that if one of them becomes fixed it varies with the other. He exhibited and described several new experiments in electricity relating to electrical induction and attraction, and expressed his opinion that the whole attractive force was dependent on the action excited in the neutral bodies reflected on the charged body. This principle, with but little modification, he further applied to any case of electrical attraction whatever.

On the Application of the Proof Plane and Torsion Balance to inquiries in Electricity. By W. SNOW HARRIS.

Mr. Harris conceives that an insulated plate of metal of small thickness may take up unequal quantities of electricity from a body and yet the distribution be uniform. The experiments in illustration of this were fully discussed.. He alluded to several laws of electrical intensity attendant on the disposition of electricity on surfaces and plates varying in extension and in length, but of the same area, and endeavoured to show that contrary to the ordinary view of electrical distribution, electricity existed on both surfaces of a hollow sphere, as well as on both surfaces of a plate of the same area. He considers every case of attraction in electricity to resolve itself into the case of charging a coated non-conducting body, and that the phænomena always correspond to those observed in the latter.

On the Aurora Borealis. By Sir JOHN Ross.

Having observed in his first arctic expedition that the aurora sometimes appeared between the two ships, and also between the ships and the icebergs, and found in his subsequent experience, both in Scotland and during the second arctic voyage, proofs satisfactory to his own mind that the aurora takes place within the cloudy regions of the earth's atmosphere, Sir John Ross states the following hypothesis on the subject, viz. "The aurora is entirely occasioned by the action of the sun's rays upon the vast body of icy and snowy plains and mountains which surround the poles."

On an economic Application of Electro-magnetic Forces to manufac turing Purposes. By ROBERT MALLET.

The separation of iron from brass and copper filings, &c., in workshops, for the purpose of the refusion of them into brass, is commonly effected by tedious manual labour. Several bar or horse-shoe magnets are fixed in a wooden handle, and are thrust, in various directions, through a dish or other vessel contain

ing the brass and iron turnings, &c., and when the magnets have become loaded with iron it is swept off from them by frequent strokes of a brush. This is an exceedingly troublesome and inefficacious process.

It appeared to the author that a temporary magnet of great power, formed by the circulation of an electric current round a bar of iron, might be substituted advantageously. The following is the arrangement which he has adopted. Several large round bars of iron are bent into the form of the capital letter U, each leg being about six inches long. They are all coated with coils of silk-covered wire, in the usual way of forming electro-magnets of such bars, and are then arranged vertically, at the interval of five or six inches from each other.

All the wires from these coils are collected into one bundle at their respective poles, and there joined into one by soldering, a large wire being placed in the midst of them and amalgamated. A galvanic battery is provided, which, if care be taken in making the junctions at the poles, &c., need not exceed four or at most six pairs of plates, of from twenty inches to two feet square. The poles of this terminate in cups of mercury, which are so placed that the large terminal wires of all the coils can be dipped into them, or withdrawn easily.

The rest of the arrangement is purely mechanical. The required motions are taken from any first mover, usually a steam engine. The previously described arrangement being complete, a chain of buckets is so contrived as to carry up and discharge over the top of the magnets a quantity of the mixed metallic particles: most of the iron adheres to the magnets, while the so far purified brass falls into a dish or tray placed beneath to receive it. This latter is also one of a chain of dishes, the horizontal motion of which is so regulated that the interval between two dishes is immediately under the magnets, in the interval of time between two successive discharges of the mixed particles on the bars.

At this juncture the communication between the galvanic battery and the magnets is interrupted by withdrawing the wires from the cups of mercury, and the result is, that the greatest part of the adhering iron drops off and falls in the space between the two dishes. The next dish now comes under the magnets, the communication is restored, and a fresh discharge from the buckets takes place, and so the process is continued.

Some iron constantly adheres to the magnets, but this is found of no inconvenience as it bears but a small proportion to the total quantity separated.

The author has had an imperfect apparatus of the sort above described at work for some time, and has found it to answer; and suggests the application of electro-magnets for somewhat analogous objects in various manufactures. He particularly mentions needle and other dry grinding.