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fide s were plus\ and Tome time after this the j, lone re- 
covered its natural fate , the plain fide being minus , 
and the convex plus. 
What appeared fingular in this experiment, was, 
that the middle fate of the fone fhould be plus on both 
fides. But we no more wonder at this, when we 
confider, that there were two caufes to produce thefe 
effects: the firft was heat, which put the fone into 
an unnatural fate (as JEpinus had obferved be- 
fore) ; for, upon cooling, it would recover its natu- 
ral fate , and confequently afford different appear- 
ances. 
But the fecond caufe, which electrified both fides 
plus when the fone was in an intermediate (or, as 
JEpinus calls it, neutral ) ff ate, between the two ex- 
tremes, was, that then the effeCts of the air itfelf took 
place, and electrified both fides plus , as it had done 
before in the 35-th experiment. 
Exp. 42. The convex fide was now prefented to 
the bellows in the fame manner, and received an equal 
number of blafts. In this experiment both fides were 
plus , but weaker than in the laft experiment ; and, 
after a time, the fone returned to its natural fate, 
affording a plus and minus appearance. 
This property in the air, of electrifying glafs, am- 
ber, See. will, in all probability, account for an ex- 
periment I met with in France , made by M. Le 
Monnier *, who fhewed me, at St. Germains en Lays , 
two or three long wires, which he had fufpended 
horizontally from the palace to his apartment, above 
* See the Memoirs of the Academy of Sciences. 
thirty 
