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LIV. A Letter fro?n Mr. B. Wilfon, F. R. S. 
and Member of the Royal Academy at 
Upfal, to Mr. iEpinus, Profejfor of Na- 
tural Philofophy in the Imperial Academy 
of Sciences at St. Peterfburg, and Member 
of the Academies of Berlin, Stockholm, 
and Erfurth. 
Read Dec. 23, 1763, jq ave not had the favour of hear- 
March.764. X m g from you li nee I fent you 
fome experiments upon Gems fimilar to thofe pro- 
duced by the Pourmalin, which induced me to con- 
clude, that the elehlnc current moves always along 
the grain thereof. It was the more agreable to 
communicate thefe new experiments to you, be- 
caufe from the lead hints the greated difeoveries 
have been made ; and what may we not expedt 
from that curious obferver of nature, who firft dif- 
covered thefe extraordinary qualities in the Pour - 
mat-in, which have fince excited the attention of fo 
many Philofophers. 
Your treatife upon this done, publidied in 1762, 
feems to be the fame you formerly mentioned in a 
letter to me. The remarks at the end of that work 
intered me in a particular manner, as they contain 
objections to feveral parts of the letter to Dr. He- 
herden. I am obliged therefore to lay fomething 
in the defence of my own experiments and deduc- 
tions, which I hope will merit your attention, and 
remove your difficulties. 
In 
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