A cork ball, on the same line and circumstances, after being electrised, was touched at the intervals of ten seconds repeatedly, for seven times, before it was exhausted. The fumes of boiling water were conveyed upon this ball after being electrised; and, after a fumigation for thirty seconds, it shewed signs of electricity, by being attracted to the approaching finger; and, after thirty seconds more, without any fumigation, it again obeyed the finger; and again, after thirty more, but at less and less distances. The same appearances occurred to me from the fumes of resin. From whence I apprehend, that Mr. Eeles, having dipped the electrised down of the juncus bombycinus in vapour for perhaps half a minute (for no time is mentioned), and finding it still retained its electric attraction, was not aware, that this same had happened, if he had by intervals touched it with his finger, or any other known conductor of electricity.
As Mr. Eeles had here objected, that there was no real opposition in the electric æther of glass, and that from wax; the common experiment to shew this was many times repeated with constant success; viz. the cork ball, suspended as above, after being electrised by the wine-glass, and repelled from it, was strongly attracted by a rubbed stick of sealing-wax; and vice versâ. In the same manner I observed the electric æther from a black silk stocking (which was held horizontally extended by the top and foot, and, being rubbed in the midst with an iron poker, was applied to the cork ball), to be similar to that of glass, and opposite to that of wax. But the following experiment appears to me to put this matter out of all doubt, and to demonstrate, that this difference is only a plus and minus of the same specific æther, and not different qualities of it, as Mr. Eeles would suppose.
A stick of dry sealing-wax was rubbed on the side of a dry wine-glass, and a cork ball, suspended as in the former experiments, played for some time between them: but glass rubbed with glass, or wax with wax, did not manifest any electric appearance. Whence it would appear, that in rubbing glass and wax together, the glass accumulated on its surface the identical æther that the wax lost. Nor is this a digression from my design: for if this opposition of the electricity of glass and wax be established, it still contributes to demonstrate the fallacy of Mr. Eeles's experiments.
But what alone would intirely destroy this electric hypothesis, is, that from the experiments of Mr. Franklin and others, the clouds are sometimes found to be electrised plus, sometimes minus, and sometimes manifest no signs of electricity at all. Whence to say an accumulation of electric æther supports these clouds, seems an assertion built upon a very unstable foundation, whose whole superstructure may well enough be termed an air-built castle, the baseless fabric of a vision.
Add to this, that Mr. Eeles, in page 140. tells us, that himself has passed thro' clouds resting on the sides of mountains. Ought not those clouds to have immediately discharged their electricity, and fallen? And common experience may remind us, that any cold bodies will condense vapour, whatever be their electric properties. So mirrors, or the glass of windows, in damp rooms, are most frequently found covered with dew; which, of all other bodies, ought most to be exempted from collecting vapours supported by electricity, as they are the least capable to attract or draw off that æther.
From all which, well examined, I am persuaded, gentlemen, you will be induced to conclude, that tho' clouds may sometimes possess an accumulation of electricity, yet that this is only an accidental circumstance, and not a constant one; and thence can have no possible influence either in the elevation or support of them. I am,
Gentlemen,
Your very humble Servant,
Erasmus Darwin.
Litchfield, March 23. 1757.
Philos. Trans. Vol. L. Tab. VI. p. 255.
