﻿770 Dr. A. Sellerio on the Repulsive Effect upon 



"by increasing the current strength over the hissing point, or 

 by shortening the length L, &c, have generally shown that 

 when the arc is not quite steady and silent, the forces acting 

 upon the poles become greater. 



6. In order to test whether the observed effect P is due to 

 any disturbance C produced by heat, as convection currents 

 of hot air, an arc was struck between two fixed carbon rods 

 A, B (fig. 2, from the Nuovo Cim.). No repulsion was 

 exerted upon a movable carbon B', although it was so 

 near to B' as to become white hot. On the contrary, the 

 influence of the heat is to cause the poles to approach each 



Fig. 2. 



w 



o 



other ; the deflexion due to C was 10 to 20 degrees, or 0'36 

 to 0*72 dyne (S., p. 70). Then if we momentarily denote 

 with O the observed effect, the true repulsion is to be set, 



p = o+c, 



j~ This disturbance is not entirely avoided by enclosing the 

 apparatus in a box, to prevent air currents, as stated by 

 Prof. Dufneld. He tried to determine the value of C, and, 

 having found approximately 0'44 dyne at 8 amp., proceeded 

 to draw a correction curve C. However, " It is unfortunate 

 that information is very difficult to obtain in the crucial part 

 of the curve, where the current is small," as he says, thus 

 we cannot yet decide with certainty whether the true repul- 

 sion P is present with the smallest currents, or whether it 

 starts up only at a current minimum. 



This interesting question is included in a general one, 



