Field at a Discharging Point. 639 



field to depend on the nature o£ the electrodes, and the 

 ■difference in the two experimental curves suggests rather 



Curves 1. 



that the determination of the critical field from the pull on a 

 liquid point is not susceptible of the same accuracy as that 

 from the pull on a metal point. 



Results at Different Pressures. 



A complete test of the theory may be obtained from 

 measurements of the mechanical force at different pressures. 

 The author rinds that some hitherto unpublished results 

 obtained a few years ago with the assistance of Miss P. M. 

 Borthwick, M.Sc, afford the necessary data. In this work 

 the experimental arrangements were as follows. 



A light cradle holding the discharge-point was suspended 

 by a fine wire bifilar inside an earth-connected metal box. 

 The rounded end of the discharge-point projected a few 

 millimetres through a hole in the side of the box: it was 

 connected to a galvanometer through one of the suspensions, 

 which were insulated from the box at the points of attachment. 

 The metal box together with a microscope for viewing the 

 discharge-point w r as placed in the vertical limb of an L-shaped 

 glass tube 3 inches in diameter, and a plate connected to 

 one pole of a Wimshurst was inserted in the other limb. 



