On the Generation of Statical Electricity. 109 
variety of opinions expressed on this subject has proceeded from 
the use of but one rubber to the cylinder, and from inattention 
to the proper method of carrying out the details of construction. 
It results from the foregoing discussion, that for large machines 
the cylinders are much to be preferred, for economy of construc- 
tion, occupying less space, being less liable to accidents, and for 
the convenient collection of the negative electricity. Plates are 
preferable for small machines, by reason of being more compact 
as well as of finer appearance, and on account of the interfering 
action of the points of the prime conductor, which emit sparks 
to the rubbers if too nearly approximated. 
te ZG 
Cylinder machines with two rubbers being thus found superior 
in many respects, when large machines are required, the above 
representation is given for reference of construction. The cyl- 
inder (A) is twelve inches in diameter and eighteen inches long ; 
it is supported by two pairs of glass pillars, (B) (B), (B)(B), one 
and a quarter inches in diameter each, and three feet long; or of 
one half this length, and joined together at the axis of the cylin- 
der by brass tubes four inches in length; these tubes being con- 
