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(for the gilt paper happened to lie with its gilded side uppermost,) it was found to terminate on the point in the gilt paper where the impression appeared, and there the impression pointed downwards. Again, when the hole in the lower part of the quire was traced from below upwards, it was found to terminate on the point in the leaf fronting the gilding, where the impression was, and there the impression pointed upwards. The facts above-mentioned seem to leave it without doubt, that the stroke had been given at the same instant, upwards and downwards; but that the electrical power from above, and from below, had seized on the gilding, dissipated part of it in vapour, and by that means become so weak, that each of them could afterwards only make an impression on the paper, marking the respective directions of their course.
Mr. S. communicated these observations to Dr. Franklin; but as no conclusion can, with certainty, be drawn but from facts, confirmed by repeated trials, he desired to have the satisfaction of making a few experiments with the Dr. in regard to this matter; to which he readily consented. For that purpose Mr. S. waited on him one morning about the middle of June; and the better to ascertain what was essential in the facts, he varied the circumstances a little from those above.
In the middle of a paper book of the thickness of a quire, he put a slip of tin foil; and in another of the same thickness he put 2 slips of the same sort of foil, including the 2 middle leaves of the book between them. On striking the two different books, the effects were answerable to what he expected. In the first, the leaves on each side of the foil were pierced, while the foil itself remained unpierced; but, at the same time, he could perceive an impression had been made on each of its surfaces, at a little distance one from another; and such impressions were still more visible on the paper, and might be traced as pointing different ways. In the 2d, all the leaves of the book were pierced, excepting the 2 that were between the slips of foil; and in these 2, instead of holes, the two impressions, in contrary directions, were very visible.
Mr. S. afterwards repeated these experiments with another similar instrument, and he met with nothing but what confirmed him in the opinion of 2 distinct counteracting powers. All the remarks he had been able to make in the repetition of experiments, that need to be added to what he had before observed, may be reduced to the 3 following.
1o. When a quire of paper, without any thing between the leaves, is pierced with a stroke of electricity, the 2 different powers keep in the same track, and make but one hole in their passage through the paper: not but that the power from above, or that from below, sometimes darts into the paper at two or more sundry points, making so many holes, which, however, generally unite before they go through the paper. What he means is, that he never yet could observe
the two powers to make different holes in the paper; but that they always keep the same common channel, rushing along it with inconceivable impetuosity, and in contrary directions. They seem to pass each other much about the middle of the quire; for there the edges are most visibly bent different ways: whereas in the leaves near the outside of the quire, the holes very often carry more the appearance of the passage of a power issuing out, and exploding into the air, than of one darting into the paper.
2o.-When any thin metallic substance, such as gilt-leaf, or tin-foil, is put between the leaves of the quire, and the whole is struck; in that case the counteracting powers deviate from the direct track, and leaving the path they would in common have taken through the paper only, make their way in different lines to the metallic body, and strike it in two different points, distant from each other about a quarter of an inch, more or less (the distance appearing to be least when the power is greatest); and whether they pierce, or only make impressions on it, in either case they leave evident marks of motion from two different parts, and in two contrary directions. It is this deviation from a common course, and the separation of the lines of direction consequent on it, that affords us the strongest proof of the exertion of two distinct and counteracting powers.
3o.-When two slips of tin-foil are put into the middle of the quire, including two or more leaves between them, if the electricity be moderately strong, the counteracting powers only strike against the slips, and leave their impressions there. When it is stronger, we generally find one of the slips pierced, but seldom both; and from what is observed in such cases, it would seem as if the power which issued from the outside of the phial, acts more strongly than that which proceeds from within, for the lower slip is most commonly pierced; but that may be owing to the greater space the power from within has to move through, before it strikes the paper.
PAPER IV. PART II. Of two Distinct Powers in Electricity.
The notion of two distinct electrical powers, acting in contrary directions, may appear to some to be the same with that of the effluence and affluence of electrical matter, which M. l'Abbé Nollet gives as the general cause of the phenomena of electricity. It may therefore be not improper to take a nearer view of these two opinions, to see how far they agree, and in what they differ.
This ingenious author had observed that when a body is electrified, a current of electric fluid issues from it, and in the form of diverging rays spreads through the air, and enters into other bodies; and that, at the same time, a current of electric fluid, issuing from other bodies, passes through the air, and in the form of converging rays enters into the body electrified. Hence he concludes, that a continued, and (to use his own terms) simultaneous effluence and affluence of 3 H
a fluid matter, extremely subtile, constitutes electricity. On this principle he endeavours to account for all the phenomena that attend the electrification of bodies.
What M. Nollet has observed with regard to two contrary currents in electricity, is by no means inconsistent with the principle of two distinct counteracting powers. On the contrary, the existence of two such currents is, according to Mr. S.'s opinion, a necessary consequence of the exertion of those powers from one body on another. It is a phenomenon of electricity only; not the principle. on which all electrical appearances depend. But a more essential difference takes place between this gentleman's opinion and Mr. S.'s: he represents the two currents as consisting but of one and the same fluid; admits but of one kind of electricity; and maintains that two bodies cannot be said to be differently electrified, but as they are electrified in a higher or lower degree. On the other hand, it is Mr. S.'s opinion, that there are two electrical fluids (or emanations of two distinct electrical powers) essentially different from each other; that electricity does not consist in the efflux and afflux of those fluids, but in the accumulation of the one or the other in the body electrified; or, in other words, it consists in the possession of a larger portion of the one or of the other power, than is requisite to maintain an even balance within the body; and lastly, that according as the one or the other power prevails, the body is electrified in one or in another manner. 1
On the Force of Electrical Cohesion. By Dr. John Mitchell. p. 390.
Dr. M. happening to be at Mr. Symmer's, he desired him to be witness to some electrical experiments he was about to make with silk stockings, of a particular kind, which he had received for that purpose. The weather was then remarkably favourable for electricity, being clear and dry, with a sharp frost, which had continued 5 or 6 days. The wind was easterly, and had been in that quarter for 10 days. It was about noon when we made our experiments: the barometer at 30, and Fahrenheit's thermometer at 32.
The stockings above-mentioned were wove of carded and spun silk, and were more substantial and weighty than those with which he had made the experiments mentioned in his 3d paper. One pair was of a deep black, having been twice dyed, to improve the colour. Another pair was of the natural colour of the silk, of a dusky white, and both new. The pair of black weighed 4 oz. 8 dwt. 4 gr., and the white 3 oz. 18 dwt. 15 gr.
They began with making a few experiments with the thin stockings formerly used: and found the result to be much the same with what is related by Mr. Symmer in his 3d paper; that is, that when the white stocking was put within the black, or vice versa, and both highly electrified, taking hold of the one,
while a scale with weights was put to the other, they could raise 17 oz. before the stockings separated. They then repeated one or two of those experiments with some little variation of circumstances. They turned one of the stockings inside out, and put that within the other; the inner or rough sides of the stockings being thus together, by which means they took faster hold of each other ; and they now found, that it required the weight of 20 oz. to separate them. When the stockings were separated, and applied externally to each other, they then raised the weight of 10 oz.
They next proceeded to try the force of electrical cohesion with the stockings of a more substantial make, viz. those above described; and there they found it to be much more considerable, as appears by the following experiments.
1o. When the white stocking was put within the black (without either of them being turned inside out) so that the outside of the white was contiguous to the inside of the black, they lifted 9 lb. wanting a few pennyweights. Now, taking the weight of the stocking to be 1 oz. 18 dwt. 15 gr. viz. the half of the weight of the pair as mentioned above, it follows that, by the force of its cohesion with the black, it raised 55 times its own weight.
2o.-When the white was turned inside out, and put within the black, their, inner or rough sides being contiguous, they lifted no less than 15 lb. 14 dwt. before they separated: so that, in this case, the single stocking raised 92 times its own weight.
3o-When the inner stocking was drawn out, and applied to the outside of the other, they lifted 1 lb.; that is, between 10 and 11 times the weight of the white stocking.
XXXVII. Some Observations relating to the Lyncurium of the Ancients. By
To determine the substance, denominated lyncurium by the ancients, has been
power like amber; and that it was said, and by Diocles among others, to attract not only straws and small pieces of wood, but also copper and iron, if beaten very thin; that it was pellucid, and of a deep red colour; and required no small labour to polish it." The rest of Theophrastus's description is taken up with the fabulous account of the generation of this stone, "that it is formed by the urine of the lynx, which the animal, as soon as it parts with it, hides, and scrapes the earth together over it; and that the stones vary according to the sex and disposition of the animal."
Dioscorides, in his History of the lyncurium, gives us only the fabulous history of its generation, before mentioned by Theophrastus; and subjoins, that it is called by some "HλExтроv πтεpuyopópoy; that is, amber, which attracts feathers to it. Pliny, in his history, disbelieves both the fabulous account of the generation of the lyncurium, as well as its attractive quality, related both by Diocles and Theophrastus, and considers the whole as a falsity; though he is candid enough to confess, that neither himself, nor any one else in that age, had seen a gem of that appellation.
Theophrastus, though more ancient, is, in most particulars, more to be depended on than either Dioscorides or Pliny. He ought to be considered much more of an original author, and one who wrote from his own knowledge than the others, who, valuable as they are, must be regarded, in most respects, as compilers. His account then of the appearance and properties of the lyncurium must be considered, in order to examine if any substance, known in our time, answers his description. But, first, it is plain that Dr. Woodward's hypothesis of the belemnites being the lyncurium, was ill founded; inasmuch as the belemnites is neither pellucid nor fit for engraving seals on, on account of the friability of its texture; neither can it, by any management, be made to attract straws, chips of woods, or other light bodies. Nor is Geoffroy's opinion less liable to exception; as amber, though it has the attractive power mentioned by Theophrastus, yet it has by no means the firm texture requisite to have seals engraved on it; neither is it so very hard, as is expressly said by this author concerning the lyncurium, as to require great labour in polishing it. Add to these, that Theophrastus has given a particular account of the history and properties of amber separately, in the before-mentioned work.
Dr. W. thinks it probable that what we now call the tourmaline was the lyncurium of Theophrastus, as it agrees with that author's description in all its sensible qualities: to wit, that it is a very hard pellucid stone, of a deep red colour; that it is very proper to engrave seals on; that it attracts, like amber, not only straws, and light pieces of wood, but filings of iron and brass, as has been lately evinced by many experiments. And that this stone, though not much attended to by us till very lately, is very common in several parts of the East Indies, and