52 



Proceedings of the Royal Irish Academy. 



a distance by a cathetometer. The whole apparatus was mounted in a room 

 of equable temperature into which direct sunlight never entered, and most of 

 the observations were made in the late afternoon. 



V —Observations of h (the rise of the smoke crossing between the fibres) 

 were made for increasing potential differences between A and B{Vi)\ that 

 between 5 and ( V^) being kept at a constant, rather high value (about 

 400 volts). In this case l/A. is proportional to the charge on the particles. 

 The curve (fig. 2) represents the type of results so obtained. 







X 



•^ 



•4 



/ 



/ 



• 



t -k 



,'-• IZ. 



■35 





•3 



^-' Fiq . 2 . 



— 1 1 i 1 1 1 



14 



l« VoUs 



All the curves display a step-like form, the explanation of which is as 

 follows : — The particles of uniform, minute size take up their charges as 

 single electrons, the number of electron charges attaching themselves to each 

 particle being dependent on the field applied. Consequently the velocities, 

 as measured by Ijh, should undergo sudden increases periodically, corre- 

 sponding to the accession of an additional electron according as the potential 

 Fi attains suitable values. Between the steps the curve should, theoretically, 

 be horizontal ; practically a certain amount of rounding-off is found, due to 

 want of uniformity of the field and other causes. The " lengths " of the 



