Mr Richardson, On an attempt to detect radiation, etc. 173 



In the form of apparatus first used the air was drawn away 

 from the wire and caused to pass between two parallel charged 

 plates. One plate was put to earth and the other was connected 

 to a sensitive gold-leaf electroscope whose rate of leak was 

 measured. The air currents were generally produced by a drop- 

 ping water bottle, but for the faster ones a water pump was used. 

 The air in entering and leaving passed through sulphuric acid 

 wash bottles, and the whole apparatus was further dried by a bulb 

 of phosphorus pentoxide inserted in the middle. The supports of 

 the plates were insulated with sulphur, and electricity was prevented 

 from leaking from the discharge wire to the plates along the glass 

 by putting an earthed ring of tin foil round both inside and outside. 

 The electroscope was enclosed in a rectangular glass box and 

 had a sulphur insulation. The movable leaf was of gold, and the 

 readings were taken by a distant telescope. Both leaves were 

 generally read in order to correct for any displacement of the 

 instrument. It was found necessary to enclose the greater part 

 of the apparatus in a wooden box to prevent leaking caused by 

 ultra-violet light and gases from the spark gap. The insulation 

 of the electroscope itself was very good, the normal leak being not 

 more than *4 scale divisions per hour, but that of the whole 

 apparatus could not be reduced below two divisions per hour. In 

 every case a blank experiment was made immediately after each 

 real experiment. For this the outsides of the jars were discon- 

 nected from the apparatus and joined by a short wire. In this 

 way the effect of the induction coil was made the same as in the 

 actual experiments. Thus any appreciable difference in the leak 

 in the two cases must be entirely due to radiation coming from the 

 wire. 



The following conditions were altered during the experi- 

 ments. 



(1) The velocity of the air varied from three small drops per 

 second out of the water bottle to a rapid continuous stream drawn 

 through by the pump. 



(2) In some of the experiments, by tightening the pinch-cock 

 of the inlet tube, the pressure of the air was reduced to about 

 5 cms. of mercury. 



(3) The material and diameter of the wires and the capacity 

 of the condensers was varied as before. 



