"1. Electricity augments the natural evaporation of fluids; since, excepting mercury, which is too heavy, and the oil of olives, which is too viscous, all the others which were tried suffered a diminution which could not be ascribed to any other cause than electricity.

"2. Electricity augments the evaporation of those fluids the most which are most subject to evaporate of themselves, for the volatile spirit of sal ammoniac suffered a greater loss than spirit of wine or turpentine; these two more than common water; and water more than vinegar or the solution of nitre.

"3 Electricity has a greater effect upon fluids when the vessels which contain them are non-electrics; the effects always seeming to be a little greater when the vessels were of metal than when they were of glass.

"4. This increased evaporation was more considerable when the vessel which contained the liquor was more open, but the effects did not increase in proportion to their apertures; for when these liquors were electrified in vessels, whose aperture was four inches in diameter, though they presented to the air a surface sixteen times larger than when they were contained in vessels whose aperture was one inch in diameter, they were, nevertheless, far from suffering a diminution proportioned to that difference.

"5. Electricity does not make any liquors evaporate through the pores either of metal or of glass; since after experiments, which were continued ten hours, there was found no diminution of their weight, when the vessels in which they were contained were well stopped."

On these experiments of the Abbé Nollet, Beccaria remarks, "The Abbé Nollet has found, by accurate experiment, that the electricity without sparks promotes the evaporation of liquids proportionally, not so much to their surface as to their natural propensity to evaporate; the real fact is this, the evaporation is not, and cannot be proportioned to the absolute surface (ceteris partibus) of liquids, but must be, and is, proportioned to the liberty of the surfaces themselves. By the words liberty of the surfaces, I mean their not being counteracted by an electricity homologous to that by which they are themselves animated." The illustrious Beccaria then proceeds to the following description of experiments which he made on the same inquiry.

"I procured small cans of tin, two inches high, cylindrical, and eight lines wide. I filled one with water, and placed it at the bottom of the electric well:* another of the cans I left in the open air, and put into it only half an inch of water, and placed it six feet distant from the prime conductor. I placed next to it a third can, entirely filled with water; afterwards I insulated both the cans and the electric well, and made them communicate with the conductor

* For a description of the electric well, see "Annals of Electricity, &c.," vol. vi. p. 415, plate v.

by iron wires that touched their bottoms. Now, neither the can placed at the bottom of the well, nor that in which the surface of the water was 18 lines lower than the brim of it, had, in three hours time, lost anything of their weight, but the can which was quite full had lost a grain, and even something more, of its weight.

"1. I suspended to the conductor one of the same cans, full of water, at the distance of three inches from the inferior surface of it, and to the bottom of this can I fastened a plate of tin, one foot wide. 2. I fixed another can on the conductor itself, which was also full. 3. I insulated two other cans, at six feet distance from the conductor; the one was on the one side of the conductor, and the other on the other side. Over the one I suspended, at five inches distance from its surface, a circular plate of tin, one foot diameter. The electricity having been continually excited for three hours together, I found that the can suspended to the conductor had lost nothing of its weight; that which was placed upon it had lost about half a grain; and that which had nothing suspended over it had lost about a grain; and the last, above which a plate of tin was suspended, had lost a grain and a half of its weight.

"Hence we see, that the evaporation was nothing where the surface of the water was counteracted on all parts by an homologous electricity. In the can placed on the conductor, only a little evaporation had taken place, because the atmosphere of the conductor bent itself over the surface of the water in that can, and lessened the evaporation. In the can placed at a great distance from the conductor, the evaporation was great, but it was still greater in the can over which the plate of tin was suspended, because a contrary electricity was actuated in that plate by the atmosphere of the can. In consequence of this, a continual dissipation of vapour was effected by invisible effluvia of the electric fire, which, through the plate were enabled to be diffused away. From the same fact we may also derive a new confirmation of the principle above mentioned, that the electric fire carries and disposes conducting (defferent) bodies in its way, &c.

"Thence we see, that the evaporation of liquids is not always proportioned to the ampleness of their surfaces; because, as the electric atmospheres of the liquids are much less counteracted by the reaction of the atmosphere of the adjacent parts, close to the sides of the vessels in which they are contained, than in other places, their evaporation must, of course, be proportionally greater.

"A number of other circumstances may also alter the quantity of electrical evaporation. 1. A square vessel will, as I have experienced, produce a greater evaporation than a cylindrical one, because the electric fire more easily dissipates through the angles of such vessels. 2. The liquor in a given vessel will evaporate the faster, as the height of its edge above the surface of the water will be in a smaller ratio to the width of it; this is because the electricity of the edge will then counteract less the electricity which promotes the

evaporation of the fluid. With regard to other circumstances, such as the temperature of the air, the dryness or dampness of the weather, &c., I think it would be needless here to expatiate upon them."

In the second edition of "Cavallo's Treatise on Electricity," page 42, we find that "electricity strongly communicated to insulated animal bodies, quickens their pulse and promotes their perspiration. If it is communicated to insulated fruits, fluids, and, in general, to every kind of bodies that are in a state of evaporation, it also increaseth that evaporation, and in a greater or less degree as those bodies are more or less subject to evaporate themselves, as the vessels that contain them are conductors or electrics, and as they have a greater or less surface exposed to the open air."

This is precisely the conclusion at which the Abbé Nollet arrived, with the exception of the extent of "surface exposed to the open air." At page 101, Cavallo states that "a considerable quantity of electricity exists in the atmosphere, and is certainly employed for some great purposes of nature." Hitherto," again he says, electricity has not been found concerned in any fermentation, evaporation, or coagulation, although the clouds, the rain, the hail, the snow, and the fogs, are almost always electrified."

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Cavallo's Treatise was published in the year 1782, and although, as appears by the preceding paragraph, the author was not aware of the fact, yet Professor Volta, of Como, had previously discovered that electricity is produced by the evaporation of water, as will appear by the following extract from the "Philosophical Transactions of the Royal Society" for 1782. Volta says,

"I mentioned, that after various attempts I at last succeeded in obtaining undoubted signs of electricity from the simple evaporation of water, and from various chemical effervescences; but as this is a fact not less interesting than new, it seems proper to subjoin in this place a faithful account of the experiments made for that purpose. The first set of experiments were made at Paris, in company with M. Lavoisier and M. De la Place, two intelligent philosophers, and members of the Royal Academy of Sciences. After I had shewn them my experiments with my condenser, they, as well as myself, began to entertain hopes of succeeding in the experiments on the evaporation, &c. Accordingly, M. Lavoisier ordered a large condenser, with a marble plane, to be made. The first experiment I attempted with this instrument, in company with M. De la Place, proved unsuccessful; but the weather at that time was bad, the room was narrow and full of vapours, and the apparatus was not quite in good order. M. De la Place and M. Lavoisier repeated those experiments in the country, and then they were attended with success, which incited us to repeat and diversify the experiments, by which means the discovery was completed; having obtained unequivocal signs of electricity from the evaporation of water, from the simple combustion of coals, and from the effervescence of iron filings

in diluted vitriolic acid. This observation was made on the 13th of April of the present year (1782), and the experiments were performed in the following manner :-In an open garden a long metal plate was insulated, which, by means of a large iron wire, was made to communicate with the metal plate of the condenser, laid on the piece of marble, which was kept continually warm by some lighted coals set underneath. This done, some chafing dishes, containing burning charcoal, were placed on the large insulated plate. The combustion of the coals was helped by a gentle wind. Some minutes after, the iron wire, by which the large insulated plate was connected with the metal plate of the condenser, was taken off; then, the metal plate being removed from the marble by its insulating handle, and presented to Mr. Cavallo's electrometer, it made the balls of it diverge with negative electricity. The experiment was repeated by placing on a large insulated plate four vessels, containing iron-filings and water, instead of the chafing-dishes; then some vitriolic acid was poured into those four vessels, sufficient to cause a vigorous effervescence, and when the strongest ebullition was going to subside, the metal plate of the condenser was removed from over the marble, and being examined, not only electrified the electrometer with negative electricity, but gave a sensible spark. At this time, having tried to obtain electricity from the evaporation of water, the effects were equivocal or hardly sensible. The same thing happened a few days after, when, however, we obtained clear signs of electricity from those effervescences, which produce fixed and nitrous air. One day the electricity arising from the evaporation of water seemed to be positive; but subsequent experiments, and other circumstances, indicate that such a phenomenon must be attributed to a mistake.

"The experiment on the evaporation of water, which did not answer so well at Paris, succeeded much better in London, where I bethought me of throwing water on the lighted coals, which were kept in an insulated chafing-dish. In this manner the electricity of the evaporation never fails to electrify the chafing-dish negatively, and strongly enough for the electricity to be discovered by the simple electrometer: it will even afford a spark, if the condenser be used. Another time this experiment was repeated with success at Mr. Cavallo's, in the following manner:-A small crucible, containing three or four small coals lighted, was insulated; then a spoonful of water was thrown on the coals, and immediately after an electrometer, which communicated with the coals by means of a wire, diverged with negative electricity.

"The experiments hitherto made, though not numerous, yet concur to shew that the vapour of water, and in general the parts of all bodies that are separated by volatilization, carry away an additional quantity of the electric fluid, as well as elementary heat, and consequently that those bodies, from the contact of which the olatile particles have been separated, remain both cooled and elec

trified negatively; from which it may be deduced, that whenever bodies are resolved into a volatile elastic fluid, their capacity for holding the electic fluid is augmented, as well as their capacity for holding common fire, or calorific fluid.* This is a striking analogy by which the science of electricity throws some light on the theory of heat, and alternately derives light from it: I mean on the doctrine of latent or specific heat, the first notions of which were suggested by the admirable experiments of Dr. Black and M. Wilkie, and which has been afterwards much elucidated by Dr. Crawford, who followed the experiments of Dr. Irwin. By following this analogy, it seems that as the vapours, on their condensing, lose part of their latent heat, on account of their capacity being diminished, so also they part with some electric fluid. Hence originates the positive electricity, which is always more or less predominant in the atmosphere when the sky is clear, viz., at the height at which the vapours begin to be condensed. Accordingly, the atmospherical electricity is stronger in fogs, in which case the vapours are more condensed, so as to be almost reduced into drops, and is still stronger when thick fogs become clouds.

"Hitherto we have accounted for the positive electricity, but it is easy to account for clouds negatively electrified; for when a cloud, positively electrified, has been once formed, its sphere of action is extended a great way round, so that if another cloud comes within that sphere, its electric fluid, agreeably to the well-known laws of electric atmospheres, must retire to the parts of it which are most remote from the first cloud; and from thence the electric fluid may be communicated to other clouds or vapours, or terrestrial prominences. Thus, a cloud may be electrified negatively, which cloud, after the same manner, may occasion a positive electricity in another cloud, &c. This explains not only the negative electricity, which is often obtained from the atmosphere in cloudy weather, and the frequent changes from positive to negative electricity, and contrarywise, in stormy weather; but also the waving motion often observed in clouds, and the hanging down of them so as nearly to touch the earth. After the forementioned discoveries, we need no longer wonder at the appearance of lightnings in the eruptions of volcanoes, as was particularly observed in the late dreadful eruption of Mount Vesuvius. The few experiments I have made, shew that the quantity of smoke, but much more the rapidity by which it is produced, tends to increase the electricity which arises from combustion, &c. How great, then, must be the quantity of electricity that is produced in such eruptions?"

It will be observed, by comparing the opinions of Dr. Franklin and M. Volta, respecting the electricity of the clouds, that they are very different to each other. Franklin considers the general electric

This is precisely the view taken by Dr. Franklin, at least 33 years previously.-EDIT.