On this metal Cronstedt has the following very curious remark: “It seems to become electrical by friction, and then its smaller particles are attracted by the loadstone; whi
2
On this metal Cronstedt has the following very curious remark: “It seems to become electrical by friction, and then its smaller particles are attracted by the loadstone; which effects are not yet properly investigated.” Zinc is an ingredient of the best amalgam for smearing the rubbers of electrical machines: But I have not been able to render a bar of zinc electrical by friction, nor to find that its smaller particles were in any state attracted by the loadstone, unless they had been scraped off by means of an instrument of iron. But, in this way, the dust of any metal is rendered susceptible of the influence of the loadstone.
3
If further experiments should establish decidedly, that the mutual contact of two different metals is absolutely necessary for the productions of Galvani’s phenomena, may not this circumstance afford an useful test of the purity of the precious metals? For instance, contractions in an animal produced by the contact of a piece of gold or silver, whose purity we wish to ascertain, with a piece of the same metal known to be pure, would then prove incontestably the presence of alloy.
4
In an able lecture, which Dr Monro lately delivered, chiefly upon this subject, he demonstrated the possibility of exciting contractions in the limb of a frog, without either of the metals he employed being in contact with it; or having any other communication with it than through the medium of some moist substance. In varying this experiment, I find, that if a frog be divided in two parts, just above the origin of the sciatic nerves, and put into a bason of water, the hind legs may be thrown into strong contractions, by bringing zinc, or tin-foil, and silver, in contact with each other, at the distance of at least an inch from the divided spine, so long as they are kept nearly in a right line with it. Water, in this case, is the only communication between the metals and the origin of the nerves.
5
The contractions produced seemed to be strong in proportion to the extent of the surfaces of the metals in contact, strongest when a large plate of zinc is laid horizontally upon a large plate of silver or gold. If the zinc be suffered to remain in contact with the silver, for a little time, the contractions of the leg cease. The zinc may then be slid over the silver, till it even touch the leg without renewing the contractions: but, in withdrawing the silver, the leg contracts at the instant the silver parts from it!
6
‘L’eau trop échauffée, ou qui est en éboullition, disperse l’électricité, de manière à en détruire les phenomènes.’
‘L’excès du froid prive l’eau même de la propriété de conduire le fluide en question.’ —Dr Valli, Lettre 9me.
7
It was in this way, indeed, that I have always excited contractions, when I have employed this new mode of influencing animals, as a test of remaining life in any part of them.
They were constantly kept in fresh water, as the situation most natural to them, during the whole of the time they were under experiment; and their skins were suffered to remain as entire as possible, since I found their muscles lost their contractile power, in a few hours, and became rigid when exposed, deprived of their skins, to the action of the water.
8
M. Fontana, in the first volume of his work on Poisons, mentions some facts, which may, to some, appear to give considerable countenance to this explanation. The microscopical eels found in dry and smutty wheat; the seta equina or gordius of Linnaeus; and the wheal polypus, all, when dry, become apparently dead: but again recover motion and life when moistened with water. One of the latter was put, by M. Fontana, upon a bit of glass, and exposed, during a whole summer, to the noon-day sun. It became so dry that it was like a piece of hardened glue. A few drops of water, however, did not fail to restore it to life. Another was, in this way, recovered after a similar exposure of a year and a half. Father Gumillo, a Jesuit, and the Indians of Peru, are quoted by the same author, on the authority of Bonguer, as speaking of ‘a large and venemous snake, which being dead and dried in the open air, or in the smoke of a chimney, has the property of coming again to life, on its being exposed, for some days, to the sun, in a stagnant and corrupted water.’
But it would almost require the credulity of an Indian to credit the testimony of the Jesuit.
