19. By repeated experiments, it was found that two spirals, formed as one voltaic element, produced a greater lifting power than three such spirals in one element; and these, again, a greater power than four such spirals joined into one element, in the proportion of the following numbers: 7284lb., 6684lb., 648lb.

3.-Experiments with very small Electro-Magnets.

In order to ascertain the excited lifting power of electro-magnets, in relation to their masses, we must employ, in the experimental inquiry, those only which are of small dimensions.

20.-An electro-magnet of thick iron wire, only of an ounce weight, covered with a double coil of thin silk-covered iron wire, lifted 3 pounds, or 300 times its own weight, when under the influence of three spirals as three electromotors, formed into a small battery.

21.-If, on the contrary, the same three spirals be united so as to form one electromotor of three times the surface, the same electromagnet lifts only 2 pounds, or a little more than 213 times its own weight.

22.-A piece of iron wire weighing 24 grains, bent into the horse-shoe form, and covered with a double coil of iron wire, lifted 9 ounces, or 180 times its own weight, when under the influence of three spirals, as three elements. In this case, both the electromagnet and the coils of wire became very hot.

23. A similar electro-magnet, weighing only of an ounce, whose poles were half a line asunder, lifted only 3 pounds, or something more than 147 times its own weight, when under the influence of three spirals, as three elements.

24. The same electro-magnet as used in the last experiment lifted only 2 pounds, when under the influence of the same three spirals as one electromotor of three times the surface.*

Results.

1. The lifting powers of the electro-magnets, compared with their masses by similar electrical currents, are in the inverse proportion to their masses. Does not the structure, which is of a more filimentous character in the iron wire, act a considerable part in giving so much greater a proportional lifting power in the small electro-magnets over that shown by the thick iron bar, whose structure is of a more granular nature?

2. By winding a copper wire of considerable thickness round the large magnet, where the resistance to conduction may be considered as nothing when compared with that presented by the electromotor, the power obtained will not gain by an increased number of elements without increase of surface; but, on the con

* In all these series of experiments, it is to be understood that when the voltaic spirals formed one element, they acted as one pair of plates. In all other cases, they formed in series.-TRANS.

trary, much will be gained by an increase of surface only, until we arrive at a certain point. But the reverse holds good in those cases with the small electro-magnets and coils of thin wire, where the resistances to conduction have a sensible relation to those of the voltaic elements, as the experiments have shewn.

3.-That so little lifting power was produced in those cases where the current was divided into six portions, each of which carried one-sixth of the whole, compared with the lifting power when the current run through the whole length of the conducting coils in sequence, is easily explained upon the general laws of influences of the resistance to conduction, according to the strength of the currents. By experiments 7 and 3, the proportions were as 984 to 4884, or nearly as 1:5. If the currents had been equally strong in both cases, the proportions of magnetic lifting power should have been as 1 : 6, because in the former case only 1-6th of the electricity operated upon each transverse section of the electromagnet. The proportion of 1:5, of course, indicates to us the proportional strength which the currents had, in consequence of the coils offering channels of six times less transverse dimensions in one case than in the other. The diminution of resistance to conduction is, however, not to be understood as appertaining to the wire alone, but also to that produced by varying the arrangement of the voltaic elements themselves, which become less, as well as that in the wire, by the partition of the latter into several channels.

4.-It remains still further difficult to understand the results in experiments 16 and 17; where, by augmenting the surface of a single voltaic element, the lifting power of the electro-magnet, instead of becoming greater, as one would have expected, absolutely became lessened. Since it would be difficult to repeat these experiments under precisely the same circumstances, any attempt of that kind ought to be attended with great circumspection. It is my intention, however, as soon as leisure permits, to carry on another series of similar experiments under a more extensive point of view, and with such apparatus at command, as to be enabled to ascertain, with ease and certainty, the least difference of lifting power that may happen to be produced.

5.-There is still something very remarkable in the augmentation of lifting power by rounding the ends of the electro-magnet. It has been stated by a philosopher, that a cross piece, with a round face, will be more forcibly attracted than one with a plane or flat well-polished face. I cannot understand, however, how the flat face should weaken the attraction just one-half on each side: I should rather suppose, that amongst the whole of the attractions on the entire plane there results an equator, in which the tangent of the vortex of the curve falls, and from which the cause of the incrcase of magnetic power might be looked for, by considering that this equator can be drawn nearer in the magnet by rounding its ends, or by rounding the cross piece. If, for instance, the distance

of the equator vary from to of a line, the lifting power would, from this cause, have its lifting power augmented about one-half.

I have above remarked, that even by raising the great lifting power of 700, 800, to nearly 900 pounds, the cross piece, when removed to about one inch from the electro-magnet, was not drawn to it, but required to be brought nearer by the assistance of the lever, before attraction took place. With respect to this fact, as well as for the general theory of magnetism, it appears to me that a foregoing series of experiments, which belong to Cramer, the mechanic, deserve still further attention. Moreover, by a closer consideration, it will not appear strange that the reverse phenomena to those shewn in my experiments, viz., the repulsive power of similar magnetic poles, is of so little value.

* Cramer's Experiments will be found at p. 460. vol. vii.-Edit.

ATMOSPHERIC ELECTRICITY.

Read by Mr. SPENCER, at the Polytechnic Institution, Liverpool.

SECTION I.

The immense number of meteorological changes that are attended with electricity have rendered the study of this agent absolutely necessary to the meteorologist. This, whenever attempted, has been rendered difficult, if not impossible, at the very outset, from the fact, that no two meteorological authorities hold opinions that are identical respecting the sources of this powerful agent. So much has this been felt, and so indefinite have been our ideas and speculations as to its origin, that my friend James Espy, of Philadelphia, in his recently published work, containing the labours and researches of years, has left electricity entirely untouched. This, at first view, might appear somewhat anomalous, and, to use a commonly quoted figure of speech, a work on meteorology without electricity might be considered as acting the play and leaving out the principal character.

The sequel, however, will show, I trust clearly, the justness of this gentleman's views as to the necassity of leaving electricity unnoticed until we have arrived at clear views respecting its proximate origin, or its functions, and the more especially, when we find another agent, whose laws and origin in the atmosphere we are able to subject to the strictest mathematical and chemical experiment, and one that is capable of accounting for nearly all the mightier changes that are constantly in operation.

In the beginning of the present year, the French Academy of Sciences were called to report on the justness of Mr. Espy's views on meteorology, and how far his theory was capable of explaining hitherto unexplained phenomena. After acknowledging the sound

ness of this gentleman's views, being founded on experiments and known facts, they recommended the study of the action of electricity in the atmosphere as being the only thing wanting to complete the whole science of meteorology.

I had long regarded the phenomena of atmospherical electricity as a favourite speculation, but nothing more. As I saw no basis on which any theory could be grounded, I had abandoned the subject almost in despair. When Mr. Espy's views on the other phenomena of meteorology became known to me, I was at once struck with their truth and beauty, and from that hour felt that any labour or research I might subsequently devote to the study of atmospherical electricity would be attended, in all probability, with results much more satisfactory than those to which I had hitherto arrived. The result, I trust, will show, that these opinions were not unfounded; but, while I state this, I have much pleasure in acknowledging, that the researches of Mr. Espy, on those meteorological phenomena that are attendant on the development of latent caloric, have cleared away the ground, and have rendered my labour much lighter than it would otherwise have been.

Evaporation has ever been considered by meteorologists to be in some way or other connected with atmospheric electricity. Until recently, however, we had no precise notion as to the manner in which evaporation itself proceeds. It was held by some of the French philosophers, that this phenomena took place from the surface of the water in the form of invisible globular balloons, having an outward casing of water, the interior being filled with caloric, which latter agent gave them their buoyancy, and caused them to ascend in the atmosphere. The globules so elaborated, when deprived of their cargo of caloric, again descended to the earth in the form of rain, hail, and snow. However satisfactory this theory might appear to the mere mathematician, it failed to satisfy chemists, who are, in general, much better acquainted with the actual changes accompanying the laws of nature than any other class of philosophical observers. Still, the matter has remained unexplained, except by mere conjecture. One of our highest and most excellent authorities, Dr. Prout, says, that evaporation takes place because the molecules of water have a tendency to rise in the atmosphere. Chemically speaking, we are unable to understand how any imperceptible actions take place in forms of bodies by the mere tendency to do so, and without any further change or combination taking place. If we are to be told, that it is a law of nature that water should rise in the atmosphere from the surface of the earth at certain temperatures, our next inquiry would be, to ascertain whether it is a mere mechanical (if, under the circumstances, we can conceive such) or a chemical change. If the latter, it necessarily involves the phenomenon of a new substance. That it is not mechanical, will be suificiently obvious when it is considered, that water absorbs about

L

1072° Fahrenheit of caloric before it will become what we somewhat erroneously term vapour. This, added to the 140° of caloric of fluidity already possessed by the water, will give us 1212° of latent caloric, which is held by this vapour in an insensible state, while the surrounding atmosphere may be 32°. It is clear, from this fact alone, that a chemical action takes place. Were it otherwise, the heat would remain sensible, as would also the water, and would heat and moisten any body passing through it. Indeed, such are the only proofs chemists ever require to ascertain the fact of chemical action having taken place: that is, whenever bodies that have entered into combination lose any portion of the properties they before held separately, or acquire new ones. Added to which, it in all cases occurs, that the result of such combinations are the production of new bodies possessing properties totally distinct from either of their constituents. The transparent aqueous vapour of the atmosphere,

then, is precisely such a body.

The errors on the subject of evaporation have arisen from not always bearing this latter fact in view. So long as it was considered that water was evaporated as water, it is obvious that no very just conclusion could be arrived at.

It has also been proved, by experiment, that unless the air is agitated, no evaporation, even at a temperature of 180°, will take place. It therefore appears clear that the vapour does not arise in globules, but arises from the surface of water in thin plates. The result, however, of the process we term evaporation, is the formation of a highly elastic and transparent gaseous substance, which chemists may, one day, term a hydrate of caloric; but we at present term it, when diffused in the atmosphere, transparent aqueous vapour, to sufficiently distinguish it from the small globules of water usually known as visible aqueous vapour. It will be seen that this body is the chief agent in the production of all those mighty atmospheric changes included in the science of meteorology. It is also the same agent that enables us to traverse the surface of the earth or water; steam being precisely this transparent aqueous vapour, or gas, that we find diffused in the atmosphere, generated within the boiler of the engine, and exerting its elastic properties, and again losing them whenever it is resolved into water by giving out its caloric of elasticity.

We have now seen that a chemical change has been effected by the production of the elastic vapour; but it also follows, that a chemical change is also produced whenever bodies are resolved back again into their former constituents. This proposition is as true as its converse.

It is now universally admitted by philosophers, that "all chemical changes are accompanied by electrical action.' Here, then, we close with the subject, all bodies being more or less charged with this mysterious agent; but it is only in what may, perhaps, be