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door, and then into the chamber, does not, as far as can be recol. lected, appear.

If indeed it could be ascertained, that the lightning, which was the death of Professor Richman, was collected on the apparatus, for this reason, because these bodies, at the instant of the light. ning, were capable of attracting and retaining the electricity, it would then be in our power sometimes to diyert the effects of lightning. But of this fact, more time and longer experience must acquaint us with the truth.

Hence Mr. Pinkney may acquaint Dr. Lining, that in Mr. Watson's opinion, at the time Professor Richman was killed, his apparatus was perfectly insulated, and had no communication with the earth, by the means of metallic or other substances, readily conducting electricity, and that the great quantity of electricity, with which, from the vastness of the cause, the apparatus was replete, discharging itself through the Professor's body, being the nearest pop-electric substance in contact with the floor, and wa unfortunately the cause of his death. This, it is presumed, would pot bave happened, had the chaio, or any other part of the appa. ratus, touched the floor, by which the electricity would have been readily communicated to the earth.

Since the reading of the above to the Royal Society, a treatise in Latin, intitled, Oratio de Meteoris vi Electrica Ortis, by Mr. Lomonosow, of the Royal Academy of Sciences at Petersburg, bas been transmitted to the Society. By this, among many other curious facts, we have been informed of certain particulars in re. gard to the death of Professor Richman; of which the following may not be improper to be inserted here.

Mr. Lomonosow observes, that with regard to the sudden death of the gentleman before-mentioned, the accounts, communicated to the public, contained some circumstances not fairly stated, and others of some importance were entirely omitted. With regard to the first, it is incontestably true, that the window, in the room where Professor Richman was, had continued shut, that the wind might have no effect on his electrometer ; but that the window in the next room was open, and the door between these two rooms, was half open ; so that the draught of air might justly be suspected to have followed the direction of the iron cod. ductor of the Professor's apparatus ; that his conductor came from the top of the house, and was continued as far as necessary. Secondly. That his conductor was not placed far from that door. case, part of which was torn off. Thirdly. That at this time no use was made of the Leyden bottle, mentioned in the preceding account; but the iron was inserted into a glass stand, to prevent the dissipation of the electrical power, and that the gnomon should show its real strength.

With regard to the second, there has as yet been po mention, that Professor Richman, at the time of his death, had seventy rubles (a silver coin) in his left coat.pocket, which by this acci. dent were not in the least altered. Secondly. That his clock, which stood in the corner of the next room, between the open window and the door, was stopped; and that the ashes from the hearth were thrown about the room. Thirdly. That many persons without doors declared their having actually seen the light. ning shoot from the cloud to the Professor's apparatus at the top of bis house. In the Phil. Trans. is given a view of the chamber, where the Professor was struck by the lightning: who stood with his head projecting towards his electrometer ; near stood Mr. Sokolow the engraver; from the door a piece was torn off, and carried forward ; part of the door-case was also rent.

In this treatise Mr. Lomonosow, among other phænomena of electricity, takes notice, that he once saw, in a storm of thunder and lightning, brushes of electrical fire, with a hissing noise, communicate between the iron rod of his apparatus and the side of his window; and that these were three feet in length, and a foot in breadth. Effects like these no one but himself has had the oppor. tunity of observing.

[Phil. Trans, 1754.

CHAP. XLIV.

ON MAGNETISM.

SECTION 1.

General Remarks on the Theory and Parts of Magnetisma. The theory of magnetism bears a very strong resemblance to that of electricity, and it must therefore be placed near it in a system of natural philosophy. We have seen the electric fluid not only exerting attractions and repulsions, and causing a peculiar distri. bution of neighbouring portions of a fluid similar to itself, but also excited in one body, and transferred to another, in such a manner as to be perceptible to the senses, or at least to cause sen. sible effects, in its passage. The attraction and repulsion, and the peculiar distribution of the neighbouring fluid, are found in the phenomena of magnetism ; but we do not perceive that there is erer any actual excitation, or any perceptible trausfer of the magnetic fluid from one body to another distinct body ; and it has also this striking peculiarity, that metallic iron is very nearly, if not absolutely, the only substance capable of exhibiting any indications of its presence or activity.

For explaining the phenomena of magnetism, we suppose the particles of a peculiar fluid to repel each other, and to attract the particles of metallic iron with equal forces, diminishing as the square of the distance increases ? and the particles of such iron must also be imagined to repel each other, in a similar manner. Iron and steel, when soft, are conductors of the magnetic fluid, and become less and less pervious to it as their hardness increases. The ground work of this theory is due to Mr. Aepinus, but the forces have been more particularly investigated by Coulomb and others. There are the same objections to these hypotheses as to those which constitute the theory of electricity, if considered as original and fundamental properties of matter : and it is additionally difficult

to imagine, why iron, and iron only, whether apparently magne. tic or not, should repel similar particles of iron with a peculiar force, which happens to be precisely a balance to the attraction of the magnetic fluid for iron. This is obviously improbable; but the hypotheses are still of great utility in assisting us to generalize, and to retain in memory, a number of particular facts which would otherwise be insulated. The doctrine of the circulation of streams of the magnetic fluid has been justly and universally abandoned, and some other theories, much more ingenious and more probable, for instance that of Mr. Prévost, appears to be too complicated, and too little supported by facts, to require much of our attention.

The distinction between conductors and non-conductors is, with respect to the electric fluid, irregular and intricate ; but in magnetism, the softness or hardness of the iron or steel constitutes the only difference. Heat, as softening iron, must consequently ren. der it a conductor; even the heat of boiling water affects it in a certain degree, although it can scarcely be supposed to alter its temper; but the effect of a moderate heat is not so considerable in magnetism as in electricity. A strong degree of heat appears, from the experiments of Gilbert, and of Mr. Cavallo, to destroy completely all magnetic action,

It is perfectly certain that magnetic affects are produced by quantities of iron incapable of being detected either by their weight or by any chemical tests. Mr. Cavallo found that a few particles of steel, adhering to a hone, on which the point of a needle was slightly rubbed, imparted to it magnetic properties; and Mr. Cou. lomb has observed that there are scarcely any bodies in nature which do not exhibit some marks of being subjected to the influence of magnetism, although its force is always proportional to the quan. tity of iron which they contain, as far as that quantity can be ascer. tained ; a single grain being sufficient to make 20 pounds of ano. ther metal sensibly magnetic. A combination with a large proportion of oxygen deprives iron of the whole or the greater part of its magnetic properties; finery cinder is still considerably mag. netic, but the more perfect oxids and the salts of iron only in a slight degree; it is also said that antimony renders iron incapable of being attracted by the magnet. Nickel, when freed from arse. nic and from cobalt, is decidedly magnetic, and the more so as it contains less iron. Some of the older chemists supposed nickel to be a compound metal containing iron, and we may still venture to assume this opinion as a magnetical hypothesis. There is in. deed no way of demonstrating that it is impossible for two sub. stances to be so united as to be incapable of separation by the art of the chemist; had nickel been as dense as platina, or as light as cork, we could not have supposed that it contained any consider. able quantity of iron, but in fact the specific gravity of these me. tals is very nearly the same, and nickel is never found in nature but in the neighbourhood of iron ; we may therefore suspect, with some reason, that the hypothesis of the existence of iron in nickel may be even chemically true. The aurora borealis is certainly in some measure a magnetical phenomenon, and if iron were the only substance capable of exhibiting magnetic effects, it would follow that some ferruginous particles must exist in the upper regions of the atmosphere. The light usually attending this magnetical meteor may possibly be derived from electricity, which may be the imme. diate cause of a change of the distribution of the magnetic fluid, contained in the ferruginous vapours, that are imagined to float in the air.

We are still less capable of distinguishing with certainty in magnetism, tban in electricity, a positive from a negative state, or a real redundancy of the fluid from a deficiency. The north pole of a magnet may be considered as the part in which the magnetic fluid is either redundant or deficient, provided that the south pole be understood in a contrary sense: thus, if the north pole of a magnet be supposed to be positively charged, the south pole must be ima. gined to be negative; and in hard iron or steel these poles may be considered as unchangeable.

A north pole, therefore, always repels a north pole, and attracts a south pole. And in a neutral piece of soft iron, near to the north pole of a magnet, the fluid becomes so distributed by induc. tion, as to form a temporary south pole next to the magnet, and the whole piece is of course attracted, from the greater proximity of the attracting pole. If the bar is sufficiently soft, and not too long, the remoter end becomes a north pole, and the whole bar a perfect temporary magnet. But when the bar is of hard steel, the state of induction is imperfect, from the resistance opposed to the motion of the fluid ; hence the attraction is less powerful, and an opposite pole is formed, at a certain distance, within the bar; and

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