228 ELECTRIFICATION OF AIR, VAPOUR OF WATER, AND OTHER GASES. 



86. At each air-pressure the electrifying needle must be raised to a certain 

 potential before the galvanometer shows any current. Thus for a pressure of 

 342 millims. no current was shown by the galvanometer at a potential of 2000 volts 

 negative ; and for a pressure of 235 millims. no current was shown at a potential of 

 1000 volts negative or 2000 volts positive. 



87. We found also that air at a. given pressure was electrified to a greater extent 

 by a certain potential of the needle than by other potentials higher or lower. Thus 

 air at a pressure of 470 millims. was electrified by the needle at 10,000 volts 1'6 times 

 more than at any other potential we tried ; while air at a pressure of 340 millims. 

 received maximum electrification, whether positive or negative, when the potential of 

 the needle was 3000 volts. 



88. We are indebted for valuable help and co-operation in the carrying out of 

 these experiments to WALTER STEWART, M.A., B.Sc., to VINCENT J. BLYTH, to 

 JOHN F. HENDERSON, to WM. CRAIG HENDERSON, M.A., B.Sc., and to W. S. 

 TEMPLETON, M.A., B.Sc. 



