and in consequence of an invitation to that purpose, he communicated a memoir of which the following is an abstract :

Pieces of camphor were cut into the form of small columns, one inch in length; a base of lead was fixed to each column; they were then placed upright in very clean saucers, and pure water poured in, to half the height of the column. Two or three hours afterwards, a horizontal notch was manifest in the column of camphor at the surface of the water; in the course of twenty-four hours, or thereabouts, by the notch becoming gradually deeper, the column of camphor was cut in two at the middle. The two pieces of the column, nevertheless, that is to say, the lower, which was immersed in the water, and the upper, in the air, suffered scarcely any perceptible diminution.

From this experiment, and others made with different pieces of camphor, kept separately in the air, in the water, and at the surface of the water, the author deduces that the most active virtue for dissolving camphor resides at that part where both the air and the water touch the camphor at the same time. Hence he explains, why, in like circumstances, camphor evaporates more quickly in a moist than in a dry air; and why the Hollanders use water in their process for subliming this substance.

It might be thought that the camphor was decomposed at the surface of the water; that the water might seize the acidifying part which renders the camphor concrete; and that the volatile part is dissipated in the atmosphere. The author rejects this notion. He thinks that water with camphor floating on its surface becomes charged with no more than a very small portion: 1. Because in these circumstances the water acquires the same taste and smell of camphor as it obtains when a small quantity of this substance is kept plunged in the same fluid. This water, by exposure to the air, loses the qualities with which it had been charged, and becomes insipid and without smell. 2. Because when the water is saturated with all it can take up, the dissipation of the camphor continues at its surface as before. 3. Because the aerial emanations of camphor made at the surface of water, do themselves crystallise into camphor.

Camphor at the surface of the water does nothing, therefore, but dissolve; and when dissolved at the ordinary temperature of the atmosphere, it is not at first in a state of vapour, as has been thought. It is simply a liquid which extends itself over the surface of water itself; and by this means coming into contact with a great surface of air, it is afterwards absorbed and evaporated. This is proved by the following facts: 1. The solution of camphor at the surface of water is more rapid in proportion to the extent of the surface. In narrow vessels, the section of the column would not be completed in a decade (ten days), even though the water might be extremely pure. 2. When the column of camphor has projecting parts, the liquid may be seen issuing by preference from certain points of the column, covering the surface of the water, and driving small floating bodies

before it, in the same manner as floating bodies go and return in a basin into which the water of a canal enters with rapidity. 3. If a small piece of camphor, already wetted at one end, be brought near the edge of water contained in a broad saucer, and be made to touch the saucer itself, it deposits a visible liquor, which is oily, and by attaching itself to the saucer destroys the adhesion between the vessel and the border of the water; so that the water retires on account of the affinity of aggregation, which not being opposed by the attraction of the saucer, causes the water to terminate in a round edge. If you remove the piece of camphor the water will not return to its place until the oily fluid is evaporated. 4. In the same manner, when the column of camphor is half immersed in the water, the oily liquor which issues forth destroys the adhesion of the water to the column, and produces a small surrounding cavity. The solution stops, or is retarded for a moment, until the fluid, extending itself over the water, becomes evaporated: the water then returns to its place, and touches the same part of the camphor; the solution begins again, and in this manner the process is effected by alternations of contact and apparent repulsion.

The rotation of small pieces of camphor at the surface of the water, is simply the mechanical effect of the re-action which the oily liquor, extending itself upon the water, exercises against the camphor itself. If the retro-active centre of percussion of all the jets do not coincide with the centre of gravity, a combined motion of rotation and progression must follow. Since the departure of the oily solu tion takes place only at the surface of the water, the rotation cannot be effected but round an axis perpendicular to the horizon; and since in similar bodies of different magnitudes the algebraic ratio of the sides to the mass increases in the inverse duplicate ratio of the sides themselves, the small particles must have proportionally more jets and must revolve more speedily than the larger.

The author reduces to one general rule all the apparent irregularities observable in the motions of the camphor. When these small parts are briskly moved at the surface of the water, if you touch this fluid with any other body, whether conductor or non-conductor of electricity, is of no consequence, provided it be well cleaned from every oily substance, in this case the motion of the camphor will not be affected. But if the same body be afterwards greased by a small drop of fixed oil, or a greater quantity of volatile oil, and then applied to the water at one extremity of the plate, you will discern a scarcely perceptible film advancing at that instant over the whole surface of the water, which will repel the small morsels of camphor, and, as if by a stroke of magic, deprive them of their motion and vivacity. One ounce of oil, poured on one extremity of a bason of

So in the original. In truth, the sides of like solids are in the inverse triplicate ratio of their solidities. This oversight of the ingenious author does not impair his deduction with regard to the velocities of rotation. N.

water of twenty feet diameter, very soon stops the motion of cam.. phor revolving at the other end. This rapid diffusion even of a fixed oil over a great surface of water, prevents the camphor from extending itself, and stops the solution and rotation of the small particles. It is for this reason, likewise, that particles of sawdust, soaked in fixed oil, begin to turn the moment they touch the water, but cannot continue their motion because the film which they form at the surface of the water is not dissipated in the atmosphere. From this last observation the author deduces this consequence, that volatility and the odorant property are not qualities necessary to produce these rotations. Volatility is merely necessary for their continuation.

At the end of his memoir the author speaks of certain other motions observed in nature, which, by the mechanism of their cause, are in some respect analogous with the motion of oily bodies at the surface of water. In bodies brought near the fire, the humidity retires always to the extremities most remote from the fire itself; because the vapour which is disengaged from the part most heated repels the rest in the opposite direction. So likewise drops of water thrown on an ignited plate of metal, remain, and are agitated in the form of a sphere; because the vapour which is produced by the contact of the plate agitates them, and does not permit them to touch the metal. By the same principle it is very easy to explain the motions of the tremella described by Adanson and Corti, which had inclined some naturalists to rank this byssus in an intermediate class between plants and animals. The tremella is a mass of very minute fibres, which being suspended in the water must be sensible to the slightest impression. It is at present known that plants when exposed to light, decompose the water in their vessels, of which they seize the hydrogen, and extrude the oxygen in the form of gas, by an operation nearly the reverse of animal respiration. If from one of the fibres of the tremella the gas issues on one side, the fibre itself must bend toward the opposite part. If, as in large trees, the gas issues from the tremella in the greatest quantity from the side of the plant which is opposite the light, the tremella must be repelled toward the source of the light itself, to which it always tends when included in an opake vessel, into which the light enters through a hole. It is not therefore necessary for the explanation of this fact, either that we should suppose any degree of animality in the plant, or attraction at a distance between the oxygen and the light. In the same manner the gas which is abundantly produced by the light of the day, becomes accumulated between the fibres of the tremella, and floats it to the surface of the water. The author takes occasion to express his acknowledgment to Citizen Fourcroy, who afforded him the means of repeating the experiments in his laboratory, and who, by his excellent lessons, informed him of the facts newly discovered since the communication between his country and France had been unfortunately interrupted.

Additions to the preceding Memoir, in a Letter from the Author to Citizen Fourcroy.

CITIZEN:

As I understand that an extract of my memoir upon the section of camphor at the surface of water, is intended to be printed, I request you will add the following facts and reflections :—

1. Dry camphor is very perceptibly volatilised under the weight of the atmosphere, at the 50th degree of Reaumer (145 Fahrenheit). It melts at the 120th degree (302 Fahrenheit), and its volatilization is then extremely rapid. In the Torricellian vacuum it rises even at the ordinary temperature of the atmosphere. This vapour has very little elasticity. It crystallizes along the sides of the tube.

2. A column of camphor is cut asunder much more speedily at the surface of boiling than of cold water. Camphor upon boiling water sublimes in great abundance with the vapour of the water itself.

3. Camphor, when floating upon water, turns and is dissipated by the contact of the oxygen, carbon, hydrogen, and azotic gases. These two last afforded more rapid movements and a more speedy dissipation. They likewise more readily dissolve carbon, phosphorus, and sulphur.

4. When camphor is burned or heated on a float at the surface of water, if it touch the liquid it gives a considerable motion to its support, but if it do not touch the water it remains motionless. The motion is not therefore produced by the simple emission of volatilized particles from the camphor. An action likewise takes place on the part of the water.

5. This action appears to me to depend on the principle of the motion of bodies which float at the surface of water, and has been explained with remarkable perspicuity by Monge. Of two small pieces of paper, twisted up and moistened, the one with the pure water, and the other with water well saturated with camphor, the first attracts and the second repels camphor on the surface of water which does not actually hold that substance in solution. Water consequently has more attraction for solid camphor, than for the little portion which it has already dissolved to saturation. It mounts along the solid piece, where it forms a curvilinear inclined surface. The small portion which is dissolved and saturated, descends along this inclined surface, and in its descent it repels backwards, by the laws of mechanics, both the surface itself and the solid particle to which it adheres. This separation of the dissolved part accelerates the dissipation of the solid piece, by affording a current of water constantly renewed. The atmosphere absorbs that part of the camphor which is already dissolved and extended on the surface of the water; the evaporation being perhaps assisted by a small portion of the water itself.

6. If a drop of oil had no affinity with the surface of the water

it would lodge itself in a small cavity; and though more elevated than the surface itself, it would preserve the globular form by its affinity of aggregation. But since it extends in a film over the water, the drop itself, or some of its principles, must necessarily be attracted in the same manner as fluids which rise along the sides of vessels.

7. Air, strongly impregnated with ether, or very hot exhalations of camphor, exercises on the small floating particles at the surface of the water a repulsion similar to that of oil, or of camphor dissolved without heat in the water itself. The former are elastic fluids, and the latter simple liquids. They must not be confounded together.

I have perhaps dwelt too long upon a subject which seems rather to be matter of curiosity, than immediate utility. But it is always a pleasure to me to embrace an opportunity of expressing my esteem and attachment to you. J. B. VENTURI.

WE have stated at page 377, that the discovery of the development of electricity by the simple contact of metals, was made by the Rev. Abraham Bennet, prior to the year 1789. This discovery, however, is subsequent to that of M. Sultzer, by applying two metals to the tongue (see page 363); but prior to Galvani's discovery of the convulsive motions of prepared frogs, by the application of metallic conductors, as stated also in page 363.

Mr. Bennet's experiments were made by means of an instrument called a doubler, which is a modification of the ordinary condenser of Volta. By the employment of this doubler, Mr. Bennet was enabled to ascertain that the simple contact of metals produces electric action. The results of this very ingenious electrician's experiments may be pretty fairly represented by the following table.

The following bodies being brought into contact with each other, and afterwards separated, produced positive and negative electric action, respectively, as below:Positive.

Negative.
Lead ore.

Mr. Bennet calls the electric action which bodies are naturally possessed of, with respect to that of other bodies, their adhesive electricity; and states that those bodies which are marked positive in the above table, have a negative adhesive electricity. His words are