C 362 ] 



Confidering the admirable fimplicity, as well as 

 the great ufefulnefs of this inftrument, it is fome- 

 thing furprizingthat the conftru&ion fhould not have 

 occurred to fome electrician before this time. Nol- 

 let's and Mr. Waits's invention of threads, projecting 

 fhadows upon a graduated board, refembled this ap- 

 paratus of Mr. Henly's, but was a poor and awk- 

 ward contrivance in companion with it ; nor was 

 Richman's gnomon, though a nearer approach to this 

 conftruction, at all comparable to it j and the in- 

 genious author of it had no knowledge of either of 

 thofe methods when he hit upon this. 



I have made a receptacle for this inftrument in my 

 prime conductor, and I have alfo a pedeftal in which 

 I can fix it j and by means of which I can very 

 conveniently place it on the wires of a battery. 



In either of thofe fituations it anfwers almoft every 

 purpofe of an electrometer, without removing it from 

 its place. 



I doubt not that you and all other electricians will 

 join with me in returning our hearty thanks to Mr, 

 Henly for this excellent and ufeful inftrument. 



Many of the effects of my battery, in breaking 

 of glafs, and tearing the furface of bodies, Mr. 

 Henly performs by a fingle jar, only increafing the 

 weight with which the bodies are preifed, while the 

 explofion is made to pafs clofe under them. 



By this means he raifes exceeding great * weights, 

 and matters ftrong pieces of glafs into thoufands of 

 the fmalleft fragments; he even reduces thick plate 

 glafs by this means to an impalpable powder. But 



* Frequently fix pounds Troy. 



what 



