52r3 
HOX. E. j. STEUTT OX THE COXHECTIYITY 
Appendix. 
Note on a Practiced Point in connection ivitli the Quadrant Electrometer. 
Most of those ^vho have had occasion to work with an electrometer of the Elliot 
pattern must have experienced the difficulty of oldaining a jar of glass that would 
insulate in a sufficiently satisfactory manner. A jar cannot he considered even 
tolerably satisfactory unless the charge takes at least a week to leak down to half its 
original value. Such jars may occasionally be met with, hut it is by no means easy 
to obtain one. It sometimes happens that a jar will satisfactorily retain a small 
charge for a much longer period than that mentioned, hut, if it be charged moie 
highly, the charge rapidly leaks down to a certain small value, after which the loss 
becomes very much less rapid. But, if the electrometer is recpiired to be highly 
sensitive, such a jar is of course useless. 
The “White Pattern” electrometers are much less suliject to this difficulty, 
because their construction allows of a great length along the glass surface between 
the charged acid and the outside coating of the jar connected to earth. And it is the 
surface leakage alone that is practically to be feared. 
After trying many jars and fiiiling to obtain a satisfactory one, I adopted an 
arrangement which has proved very convenient as a substitute. A short hi ass 
]jillar a (fig. 3) carries a circular lirass disc c. On to <c a round ebonite plate of the 
same diameter is fixed by means of three screws. The heads of these screws are on 
the underside of tlie brass plate, and they pass into tapped holes m the eliomte, 
which do not pass right through it. The outside of this ebonite disc is ^ inch thick. 
