408 Proceedings of Royal Society of Edinburgh . [sess. 
supported by its ends on small blocks of paraffin so situated as not 
to be shone on by the Rontgen rays. This insulated metal was 
connected by a copper wire to the insulated terminal of the electro- 
meter. To protect it from inductive effects it was enclosed in a 
lead tube connected to the other terminal and to sheaths (see 
diagram 4). 
The Rontgen lamp was placed in a lead cylinder connected to 
sheaths. The rays passed into the tube of aluminium through a 
window in the lead cylinder, which could be screened or unscreened 
at will, as described in § 1. 
The course of the experiment was the same with each insulated 
metal. The metal was charged first positively, then negatively ; 
the Rontgen rays were then shone on it through the aluminium 
cylinder surrounding it, and the electrometer readings taken at 
fixed intervals, until a steady reading on the electrometer was 
obtained. The point at which the electrometer reading remained 
steady with the rays acting we shall call the rays-zero. 
Finally, the insulated metal was discharged by metallic connec- 
tion in the electrometer, and re-insulated; the rays were again 
shone on it until the rays-zero was again reached. 
The following figures, taken from the laboratory book, show the 
effect obtained in this way when the insulated metal was amalga- 
mated zinc. 
