"XlV 
On the Method of rendering very fenfbie 
especially when they are hot ; hence there is no occafion ta 
warm them, when they are good for the purpoie, left they 
lhould he fo well prepared as to be ealily excited, and then adt 
like an eledlrophorus. 
19 However, the advantages which a varnifhed plate has 
above the common eledlrophorus are, 1. that the varnifh is 
always thinner than the common relinous ftratum of an eledtro- 
phorus. 2. That the varnifh acquires a more fmooth and plain 
Surface ; hence the metal plate may be more eafily, and to 
more advantage, adapted to it. 
20. Inftead of the above mentioned plane of marble or metal- 
varnifhed, there may be Substituted, with equal advantage, any 
Sort of plane covered with dry and clean oil-cloth or oil- 
ill k or fattin and other Silk-fluff that is not confiderably 
thick ; which will anfwer very well, without requiring any 
more than perhaps a flight warming. The filk-fluffs anfwer 
better for this purpofe than thofe made of cotton or wool, and 
thefe better than linen. However, by a previous drying and 
keeping them hot during the experiment, paper, leather, wood, 
ivory, bone, and every Sort of imperfedl condudlor, may be 
made to anfwer to a certain degree. 
2 r . If thofe imperfedfly condudling Subfiances were dried 
too much, then they would become quite eledlrics, and conse- 
quently ulelefs for our purpofe (as will be made appear 
better in the Second part ot this paper), excepting when they 
were ufed like refins, &c. 
22. 1 mufl not omit to mention alfo, that the apparatus may 
be rendered more Simple by applying the filk or other femi- 
condudling Stratum to the upper, viz. to the metal plate, which 
is furnifhed with a glafs handle inftead of the marble or other 
plate, which in that cafe becomes ufelefs: for in its ftead a 
plane of any kind may be ufed, Such as a common wooden or 
marble table, even not very dry, a piece of metal, a book, or 
other condudlor, whether perfect or imperfedt, it being only 
neceflary that its Surface be flat. 
In fadl, nothing more is requifite for our experiment than 
that the eledlricity, which tends to pafs from one Surface to the 
other, 
