Mr Richardson, On an attempt to detect radiation, etc. 175 
of the wire ff 1 to the testing system hg an earthed ring of tin 
foil was put round the outside of the glass tube at d ; and inside 
a fine steel spiral c which pressed tight against the glass was 
supported by the stout copper wire k. The wire as passed of 
course down the axis of this spiral. The lower part of the 
apparatus was protected from spark gases and ultra-violet light 
by being enclosed in the cigar-box h. It was found necessary to 
protect also the upper part of the apparatus from ultra-violet 
light. This was done by a cardboard arrangement p built to fit 
it. The air was exhausted through the tube n which led by way 
of a phosphorus pentoxide bulb to a Topler pump and McLeod 
gauge. 
