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of the equator vary from too to sto 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.
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 frèm 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 maihematician, 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 suiticiently obvious when it is considered, that water absorbs about
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
termed its free state that it becomes evident to our instruments or senses. Among bodies water would seem to possess it in greatest quantity. Faraday and others have demonstrated, that there is as much electricity locked up in a grain of water as would cause an ordinary thunderstorm. The electricity contained in the water, apparently by the law of its composition, may, for convenience sake, be termed its latent electricity, and that which exists on aqueous surfaces, for the same reason, be termed specific electricity. When evaporation takes place at the surface of the water, being, as we have seen, a chemical change, the electrical equilibrium of this body is disturbed. According to experiments made by myself and others, this disturbance is of a decidedly negative character ; but, as my object is more to account for the real or positive electricity that exists in the atmosphere, than to explain the phenomena attendant on the absence of it in the free state, usually termed negative electricity, I merely allude to the fact.
Let us now assume the evaporation as having taken place, and the elastic gaseous vapour diffused pretty equally throughout the atmosphere ; but, for this diffusion, it does not require us to suppose that it possesses a superior levity to raise it, in the first instance, from the surface of the water, and then elevate it to the higher regions of the atmosphere. The currents of air that always agitate the water liberate the thin plates of the nascent substance from the surface.
We must now search for another law of nature to explain its diffusion, it being nearly alike over vast spaces.
Fortunately, in the present state of science, this is easily found. The “law of diffusion that exists among all gaseous bodies, no matter what their specific gravity, first noticed by Dr. Dalton, and since investigated, in the most masterly manner, by Professor Graham, at once points out that the elastic gaseous vapour of water is governed by this law, in common with all other gaseous bodies. Were it to be governed by the laws of gravity, it would only be found in the higher regions of the atmosphere, it being 625—air being 1,000. This elastic vapour, then, fills the higher as it does the lower regions of the atmosphere.
Observation has shown us that the temperature of the atmosphere falls one degree of Fahrenheit for every hundred yards above the level of the sea, varying a little, more or less, with the climate and
Dr. Dalton and Gay Lussac have shewn, that when the dew point is 80° Fahrenheit, and the barometer stands at thirty inches, the quantity of elastic vapour held in solution in atmospheric air is nearly the 48th of its whole weight and 1-30th of its bulk.
Let us pause for a moment, and review what is already said. First, evaporation is constantly taking place from the surface of the water, and when we take into consideration the immensely large proportion of aqueous superfices possessed by our planet, it will at once
point out the immense quantity of water that is daily abstracted from its surface. I have also said, that water, when taken up into the atmosphere by means of evaporation, is water no longer ; but, by virtue of its combination with about 1,072 degrees of Fahrenheit of caloric, it becomes a gas possessing properties of its own, under certain circumstances possessing neither aqueous nor heating properties, just as we find in chemistry, that when an acid and an alkali combine they form a salt possessing totally distinct properties from either of their constituents. We have also seen, that, in accordance with the law of the diffusion of gaseous bodies, this substance must be pretty equally diffused throughout the atmosphere.
The experiments of Dalton and Gay Lussac prove this, and, indeed, those of all subsequent observers, to the average extent of 1-48th of its whole weight and 1-30th of its bulk.
These proportions are immense, and may slow us the magnitude of the functions of this agent when mingled with the other gases the atmosphere. I may here add, in parenthesis, that popular writers on physics, when speaking of the constitution of the atmosphere, will never convey correct notions on this subject, unless they enumerate aqueous vapour among the gases that constitute the air we breathe, it being of as much importance as any of the others, and, without it, it is difficult to see how any of the functions of animal or vegetable life could be performed.
It is true formula have been given by Mr. Daniels and others, by which we may calculate the amount of steam in the atmosphere, at certain barometrical pressures, combined with a given temperature, as thus, that the specific gravity of transparent aqueous vapour to atmospheric air is as 0·620 to 1.000. Suppose, then, we were to take 100 cubic inches of atmospheric out of a temperature of 60 Fahrenheit, and a barometrical pressure equal to 30 inches, we would find the whole to weigh 31 grains. But, suppose we wish to carry the inquiry still further, and find the actual amount of what is somewhat erroneously termed dry gas contained in the already given quantity of atmosphere, we should then find, that the 100 cubic inches had diminished in volume equal to 98.14; consequently, the transparent aqueous vapour, in such a quantity, would have a volume equal to 1.86 cubic inches. In like manner it would, also, be found, that the weight, 31 grains, had been reduced to 30.65, making the weight of 1.86 cubic inches of aqueous vapour equal to 0.35 grains. The term dry, applied to the other gases of the atmosphere, leads us to suppose, that the transparent aqueous vapour is really wet, when, in fact, such is not the case, as, before it will give out its water as such, a really chemical change must take place.
Bearing in view the preliminary remarks on evaporation and the gaseous constitution of the atmosphere made in the former sec