424 PHILOSOPHICAL TRANSACTIONS. [aNNO 1753, 



Exp. 8. — Having made the Torricellian vacuum about 5 feet long, after the 

 manner described in the Phil. Trans, vol. xlvii. p. 3/0, or p. 236 of this vol. of 

 these Abridgments, if the excited tube be brought within a small distance of it, a 

 light will be seen through more than half its length ; which soon vanishes, if the 

 tube be not brought nearer ; but will appear again, as that is moved farther oft'. 

 This may be repeated several times, without exciting the tube afresh. 



This experiment may be considered as a kind of ocular demonstration of the 

 truth of Mr. Franklin's hypothesis ; that when the electrical fluid is condensed 

 on one side of thin glass, it will be repelled from the other, if it meets with no 

 resistance. According to which, at the approach of the excited tube, the fire is 

 supposed to be repelled from the inside of the glass surrounding the vacuum, 

 and to be carried off" through the columns of mercury , but as the tube is with- 

 drawn, the fire is supposed to return. 



Exp. Q. — ^Let an excited stick of wax, of 24- feet in length, and about an inch 

 in diameter, be held near its middle. Excite the glass tube, and draw it over 

 one half of it ; then, turning it a little about its axis, let the tube be excited 

 again, and drawn over the same half; and let this operation be repeated several 

 times ; then will that half destroy the repelling power of balls electrified by glass, 

 and the other half will increase it. 



By this experiment it appears that wax also may be electrified positively and 

 negatively. And it is probable, that all bodies whatever may have the quantity 

 they contain of the electrical fluid, increased, or diminished. The clouds he has 

 observed, by a great number of experiments, to be some in a positive, and others 

 in a negative state of electricity. For the cork balls, electrified by them, will 

 sometimes close at the approach of excited glass ; and at other times be separated 

 to a greater distance. And this change he has known to happen 5 or 6 times in 

 less than half an hour ; the balls coming together each time, and remaining in 

 contact a few seconds, before they repel each other again. It may likewise easily 

 be discovered, by a charged phial, whether the electrical fire be drawn out of the 

 apparatus by a negative cloud, or forced into it by a positive one : and by which- 

 ever it be electrified, should that cloud either part with its overplus, or have its 

 deficiency supplied suddenly, the apparatus will lose its electricity : which is fre- 

 quently observed to be the case, immediately after a flash of lightning. Yet 

 when the air is very dry, the apparatus will continue to be electrified for 1 or 

 15 minutes, after the clouds have passed the zenith; and sometimes till they 

 appear more than half-way towards the horizon. Rain, especially when the 

 drops are large, generally brings down the electrical fire ; and hail, in summer, 

 he believes never fails. When the apparatus was last electrified, it was by the 

 fall of thawing snow ; which happened so lately as on the 1 2th of November ; 

 that being the 26th day, and 6 1st time, it has been electrified, since it was first 



