130 ELECTRICITY. 



tricky, ensue. Beccaria verified this hypothesis by experiment. He con- 

 structed a glass siphon, in one leg of which air was enclosed above a column 

 of mercury, and compressed by the column in the other leg of the siphon. On 

 discharging a Leyden jar through the air thus enclosed, the column of mercury 

 in the other leg was suddenly elevated, and recovered its position after several 

 oscillations.* This fact was also noticed by Kinnersley, the friend and asso- 

 ciate of Franklin, but not until a later period. 



This was afterward corroborated by Bouguer and De la Condamine, when 

 they encountered a violent thunder-storm on one of the highest mountains of 

 Peru. The cloud from which the thunder proceeded was placed at but a small 

 distance above their heads. The thunder heard by them consisted only of 

 single cracks, or explosions, like those which attend the discharge of electric 

 batteries ; an effect manifestly produced by the proximity of the cause of the 

 sound, and the highly rarefied state of the air at that great elevation. 



Contemporaneously with Beccaria, Franklin, and Canton, the subject of at- 

 mospheric electricity engaged the attention of Lemonnier, who erected an ap- 

 paraWis according to Franklin's method at St. Germain-en-Laye, with which he 

 showed that sparks were received from the conductor not only in times of 

 storm, but also when the heavens were cloudless. He also first showed that 

 the electricity of the air underwent every twenty-four hours periodical varia- 

 tions of intensity. 



Beccaria determined the law of these variations, and was the first who dem- 

 onstrated that at all seasons, at all heights, and in every state of the wind, the 

 electricity of an unclouded atmosphere is positive. He found no indications 

 of electricity in the air in high winds, when the firmament was covered with 

 black and scattered clouds, having a slow motion in a humid state of the air ; 

 but in the absence of actual rain, he found that in changeable squally weather, 

 attended with occasional showers of snow, hail, or rain, the electricity was very 

 variable, both as to its quantity and quality, being sometimes feeble and some- 

 times intense, sometimes positive and sometimes negative. 



Contemporaneously with Beccaria in Italy, Canton prosecuted inquiries in 

 many respects similar in England, and in various matters of minor importance 

 these philosophers arrived at the same results. The most considerable dis- 

 covery due to Canton was, that the electricity developed in the friction of the 

 same substance is not always of the same kind. It will be remembered that 

 Duiaye gave the names vitreous and resinous to the two fluids, on the supposi- i| 

 tion that each was invariably produced by the friction of the classes of bodies Ji 

 signified by these terms. Canton, however, showed that glass itself was ca- i 

 pahle of being electrified negatively, and would be always so electrified, if the 

 rubber used were the fur of a cat. Canton also (as well as Beccaria) proved 

 that a volume of air in a quiescent state might be charged with electricity. To 

 Canton is also due the discovery of the virtue of the amalgam of tin and mer- 

 cury, still used with so much effect to augment the development of electricity 

 on glass. 



The progress of the science had now attained a point at which the great 

 principle of induction could scarcely fail to force itself upon the notice of those 

 engaged in electrical researches. A natural law of the highest order, embra- 

 cing within the range of its application nearly the whole domain of electrical 

 phenomena, its discovery and development, forms an epoch in the history of 

 the science, scarcely second in importance even to that by which Franklin 

 brought meteorology within the legislation of electricity. How much, then, 

 will the veneration in which the memory of the philosopher of the West is 



* Beccaria, Elettricismo Artificiale. Turin, 1753 : p. 227. 



