t 2 S 5 ] 
XVI. Defcription of a new Electrical Injirument capable of col- 
lecting together a diffufed or little condenjed Quantity of Elec- 
tricity. By Mr. Tiberius Cavallo, F . R. S. 
Read April io, 1788. 
O NE of the principal defiderata in practical electricity has 
been a method of afcertaining the prefence and quality 
of luch diffufed or weak eleCtricity as could not inr mediately 
affeCt an eleCtrometer ; of this nature is the electricity pro- 
duced by effervefcences and other proceffes, the eleCtricity of 
the atmofphere in ferene and warm weather, &c. 
M. Volta’s condenfer, which is defcribed in Volume 
LXXII. of the Philofophical TranfaCtions, was the firft at- 
tempt of the kind, and, indeed, when this inftrument is in 
good order, it anfwers exceedingly well ; but the difficulty of 
conftruCting and of preferving it, added to the frequent uncer- 
tainty of the refult (it being difficult to fay, whether in cer- 
tain cafes the eleCtricity obtained comes from the inftrument 
itfelf, or from the fubftance in queftion) have occafioned its 
being little, if at all, ufed by thole who ftudy the fubjeCt of 
eleCtricity. 
Mr. Bennet’s doubler, which is defcribed in Volume 
LXXVII. of the Philofophical TranfaCtions, was alfo in- 
tended to manifeft fmall, and otherwife un perceivable, quan- 
tities of eleCtricity ; but from the experiments and oblervations, 
which I had the honour of laying before the Royal Society in 
November laft, it feems to be clearly (hewn, that this dou- 
bler 
