404 Proceedings of Royal Society of Edinburgh. [sess. 
meter. In all the experiments to he described, B remained the 
same. 
It consisted of a cylindrical lead can, 25 cms. long, 4 cms. 
diameter. A metal bar about 1 cm. diameter, 25 cms. long, was 
supported centrally on paraffin filling the whole space between it 
and the containing lead. This metal bar was connected by a 
wire to the internal coating of A. To protect this wire from 
inductive effects, it was surrounded by a tube of lead connected 
to sheaths. 
The Leyden A, which was placed opposite the Bontgen lamp, 
was different according as we were experimenting on the dis- 
charge through air, through paraffin, or through glass. 
To get a definite difference of potential, the two pairs of quad- 
rants of the electrometer were first placed in metallic connection. 
Then one terminal of a battery or of an electrostatic inductive 
machine was connected to the internal coatings of the jars, and 
the other terminal to sheaths. The difference of potential pro- 
duced was measured by a multicellular voltmeter in the case of 
differences under 500 volts, and on a vertical single vane volt- 
meter for higher differences. 
When the desired difference of potential had been established, 
the metallic connection of the battery or electric machine with 
the internal coatings of A and B was broken, and this charged 
body left to itself. To find the loss due to imperfect insulation, 
the pair of quadrants in metallic connection with the outside coat- 
ing of B was insulated in the ordinary way, and the deviation of 
the electrometer reading from the metallic zero per half-minute 
was observed. To find the loss when the rays were acting, the 
two pairs of quadrants were again placed in metallic connection, 
the Bontgen lamp set a-going, then the pair of quadrants con- 
nected to the outside coating of B was insulated from the other 
pair, and the deviation from metallic zero again observed per 
half-minute. 
§ 14. In the experiments with air, the Leyden A consisted of 
an aluminium cylinder, 16 cms. long, 3 cms. in diameter. This 
cylinder projected beyond the left tube, and was connected to 
sheaths. The insulated metal inside it, which was a flat strip of 
aluminium, about 10 cms. long and 1J cms. wide, cut from the 
