[ 3^2 ] 
Confidering the admirable flmplicity, as well as 
the great ufefulnefs of this inffrument, it is fome- 
thing furprizing that the conffruCtion 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 comparifon with it ; nor was 
Richman’s gnomon, though a nearer approach to this 
conftru&ion, at all comparable to it ; and the in- 
genious author of it had no knowledge of either of 
thofe methods when he hit upon this. 
J have made a receptacle for this inftrument in my 
prime conductor, and I have alfo a pedeftal in which 
I can fix it; and by means of which I can very 
conveniently place it on the wires of a battery. 
In either of thofe fituations it anfwers almofl 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 prefled, while the 
explofion is made to pafs clofe under them. 
By this means he raifes exceeding great * weights, 
and Shatters 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 
