398 Scientific Proceedings, Royal Dublin Society. 



motive force. Besides, in most of such experiments it is unlikely that a 

 critical velocity is reached. The effects of turbulent motion miglit, however, 

 become of importance in sucli work when higher velocities are used. 



I have to thank Professor McClelland, f.r.s., for suggesting this research, 

 and also for the interest lie has taken in its progress. To him and to the 

 Royal Dublin Society my thanks are due for the use of the radium 

 employed. I have also pleasure in recording here my indebtedness to 

 Mr. J. J. Nolan, m.a., Assistant in tlie Piiysics Department of University 

 College, for devoting much time to assisting me during many of the measure- 

 ments, which were difficult to carry out single-handed. 



