VOL. LXIX,] PHILOSOPHICAL TRANSACTIONS. 60l 



and under end of each flat board, in order to keep them steady in their vertical 

 situation. A female screw, turning on these horizontal male screws, was placed 

 between each of the fiat boards at their upper and under extremities, and served 

 to bring each of the discs as near in contact with the hares' skins as was required 

 to receive a proper friction. 



The 3 paste-boards were fixed in the frame, and whirled round. The elec- 

 tricity excited was so strong that I took sparks between i and 2 feet long from 

 the front surface of the first disc by approaching my knuckle to it. I then ap- 

 plied a tin conductor to it, about 6 feet long and 6 inches diameter, divided into 

 2 branches ; the extremities of which were furnished with a thick silver lace 

 fringe, instead of points. The sparks from this conductor were about 4 or 5 

 inches long, appeared to be very thick, were very brilliant, and so strong, that I 

 did not chuse to receive many of them ; nor did those who came to see the ma- 

 chine care to receive more than one. As these sparks succeeded each other at 

 short intervals, I think they would have been much longer if every thing had 

 been adapted for that purpose ; as I saw afterwards done at Mr. Nairne's, who 

 contrived to obtain sparks of 20 inches long and upwards, from a large glass 

 cylinder. 



I considered this paste-board machine rather as a rough sketch of an apparatus, 

 by which I conceived the hope of obtaining an electrical power of almost any 

 degree required, than as a complete machine. My intention was to find out a 

 contrivance by which a very great quantity of electrical fire might be collected 

 without great expence, and without much danger of breaking the apparatus, 

 which two articles cannot be avoided when we make use of uncommon sized 

 glass cylinders or discs. 



I saw, two years ago, at the duke of Chaulnes at Paris, an apparatus which 

 had a plate glass 5 feet diameter. This alone cost him 800 French livres. As I 

 had not adapted the tin conductor to receive the electricity from the 3 discs, but 

 only from the front disc, I cannot tell whether the force of electricity would 

 have been proportionably stronger if I had made some metallic communication 

 between each of the discs. I found, that the apparatus, as it was constructed, 

 could not easily have admitted more than 3 such large discs ; for the 12 surfaces 

 exposed to friction being each a foot and a half long, and above 3 inches broad, 

 made so much resistance to the working of the machine, that it required a 

 strong arm to work it. Being satisfied with having found that by this, or a con- 

 trivance of the same kind, a much greater power could be excited than by the 

 common glass apparatuses ; I did not chuse to put myself to more trouble or ex- 

 pence to increase the strength of its frame, or the number of discs. 



I must observe, that such a machine may be kept in good order in a heated 

 room ; but that it will soon lose its force in countries where it is not the custom 



VOL. XIV. 4 H 



