C 288 ] 
XXVII. An Account of a Doubler of EleCtricity, or a Machine 
by which the leaf conceivable Quantity of pofitive or negative 
Electricity may be continually doubled ', till it becomes perceptible 
by common Electrometers , or vijible in Sparks. By the Rev. 
Abraham Ben net, M. A . ; communicated by the Rev. Richard 
Kaye, LL.D. F. R. S. 
✓ 
Read May ic, 1787. 
T HE great importance of a machine for the pnrpofe of 
detecting very minute quantities of eleCtricity has oc- 
curred to many of the cultivators of this fcience ; as by fuch 
an afliRant not only many chemical combinations or folutions, 
but alfo many yet unexplained atmofpherical phenomena, may 
become intelligible. 
The labours of M. Volta have been very fuccefsful on this 
fubjeCt by the application of his condenfer (as he terms it), 
which, by means of a thin- coated electric, is capable of re- 
ceiving a greater quantity of the electrical fluid than a com- 
mon inl'ulated conductor, and rendering it perceptible by fepa- 
rating the pofitive and negative fldes of the charged plate. On 
this ingenious contrivance Mr. Cavallo made a very confi- 
derable improvement by transferring the received quantity of 
eleCtricity from a larger to a fmaller condenfer, as explained in 
the Phil. Tranf. Vol. LXX1I. 
Notwithftanding the very great fenfibility of this apparatus, 
the eleCtricity of the atmofphere is fometimes too weak to be 
dilcoverable by it : for inRance, in fome fhowers, when the 
negative Rate of the falling rain is nearly equal to the pofi- 
tive Rate of the air. Add to this the trouble of keeping an 
infulated and elevated conductor fufficiently dry, and the dan- 
ger 
