598 PHILOSOPHICAL TRANSACTIONS. [aNNO 1779- 



XXXIX. Improvements in Electricity. By John Ingcnhouz, F. R. S. Body 

 Physician to their Imperial Majesties. IVho was nominated by the President 

 and Council to prosecute Discoveries in Natural History, pursuant to the JVill 

 of the late Henry Baker, Esq., F. R. S. p. 659. 



It is now about 15 years since I began to make use of flat glasses, instead of 

 globes or cylinders, to excite electricity. Finding that a greater quantity of 

 electricity could be excited on a flat piece of glass, when rubbed on both sur- 

 faces, than when it was only exposed to friction on one side ; I thought it would 

 be an advantage to substitute a round plate, or disc, of glass, for a globe or 

 cylinder. I also thought another material advantage might be derived from a 

 plate of glass, as the form of it admits of placing cushions or rubbers on different 

 parts of it, and taking the electricity, excited by these rubbers, from the inter- 

 stices between them, which cannot conveniently be done when a globe or cylin- 

 der is used. The only inconvenience which I at first conceived would ensue from 

 it was, that the centre on which the plate was to be fixed and whirled round, 

 would always be too near the rubbers, unless these were very short, or the plate 

 of a considerable size ; and that these would throw the electricity, collected on 

 the surface of the glass, on that very centre. To obviaie this difficulty, I pro- 

 posed to make the centre also of glass, or some other non-conducting substance, 

 as baked wood. 



I began first by making use of one of those glass stands, called a waiter, and 

 which has a glass support fixed at right angles to its centre. I whirled the 

 waiter round as well as I could, rubbing it sometimes on one side, sometimes on 

 both. In this imperfect state I showed it to Dr. Franklin, who approved much 

 of the scheme, and advised me to pursue it. Soon after, I showed it to several 

 of my acquaintance, and in a short time I found such machines ready made at 

 Mr. Ramsden's, and at some other mathematical instrument makers. Since 

 that time great use has been made of these electrical plate machines throughout 

 Europe, as they were thought by many to be more powerful in a little compass 

 than those with globes and cylinders. 



In my travels through different countries, I now and then met with consider- 

 able improvements made in them. Abbe Fontana had contrived one for the 

 cabinet of the great duke of Tuscany, which consisted of 2 plates, of J 8 inches 

 diameter, fixed to the same centre, and each rubbed on both sides on 2 opposite 

 places. The electrical fire excited on these joint plates, when forced on a cour, 

 ductor divided in 2 branches to receive it, was very powerful ; so much so, that 

 the conductor, being unable to contain the whole, threw it back upon the brass 

 centre ; from which it passed to the hand of the operator, and gave him a very 

 disagreeable shock. ^ 



Mr. Cuthbertson, an ingenious matl\ematical instrument maker at Amsterdam. 



