4 Mr. Cavallo’s Obfervaiions on 
two extremities of a linen thread, the middle of which was 
fattened to an oblong wooden box, in which the thread and 
bails were kept, when not actually in ufe. It was with fuch 
an inttrument that Mr. Canton himfelf, Father Beccaria, 
and others, alcertained the electricity generally exitting in the 
air; and that Mr. Rona yne difcovered the conttant eleCtricity 
of fogs. But in the courie of my experiments, having made 
frequent ufe of fuch electrometers, it naturally occurred to 
me, that in feveral cafes, when the electrometer gave no figns 
of electricity, or at leatt not fufficient to afcertain its quality, 
the caufe of it was the refpectively large fize of the inttru- 
ment ; for a fmall quantity of electricity being diffufed through 
the box, thread, and balls of the eleCtrometer, had not pow r er 
fufficient to feparate the balls, and of courfe to (hew its pre- 
fence. In conlequence of this, I contracted the fize of the 
electrometers to fuch a degree as could be affeCted by lefs than 
the tenth part of that quantity of eleCtricity which was ne- 
ceflary to affeCt Mr. Canton’s eleCtrometer. But in making 
the electrometers very ffiort, the ttiffnefs of the threads, which 
had been infignificant in a great extent, became now very con- 
fiderable ; hence, inftead of fattening the balls to the two ex- 
tremities of one piece of thread, I found it neceflary to fuf- 
pend each ball by a feparate piece of thread, the upper part 
of which was formed into a loop, which moved in a ring of 
brafs wire. 
The electrometers, thus improved, were frill fubjeCt to a 
very great imperfection, which was the twitting of the threads ; 
to avoid which I fubttituted fine filver wire, inttead of linen 
threads, which anfwered very well. However, in obferving 
the eleCtricity of the atmofphere, thofe electrometers appeared 
to labour under a confiderable inconvenience, which was their 
4 being 
