Strain atony the Linen of Force. 

 Tube 9. — Adherent Armatures. 



G93 



Spark- 

 length. 



Potential. 



Mean elong. 

 mior. cliv. 



Mean elong. 

 WxMK 



Time. 



5'0 mm. 



60 CG.S. 



350 



210 



025 min. 



5-0 



60 



62-5 



37o 



1-00 



5-0 



60 



67-5 



4-05 



2-50 



7-5 



85 



67-5 



4-05 



025 



Greater potentials could not be used as the tube was 

 raptured with that spark-length. The tube could of course 

 be repaired and used again. 



According to the theory, the elongation varies inversely as 

 the square or the thickness, thus for the same potential the 

 ratio of the deflexions of tubes 7 and 9 should have been 

 three to eight. This is not verified, as the deflexions for 

 equal potentials and time of charging are about equal. In 

 fact, the effect I ascribe to heating is so preponderant as to 

 overshadow all others. 



Tube 8. — Paraffin, Adherent Armatures. 



While experimenting with paraffin tubes the potentials 

 were carried to the breaking point, which occurred at a 

 spark-length of 10 mm., or 110 c.G.s. I observed no changes 

 of length at all. I think that experiments with this substance 

 have little significance as it is so viscous that not much could 

 be relied upon. 



JS on- Adherent Armatures. 



The tinfoil was removed from the tubes and the non- 

 adherent brass-tube armatures were mounted in place. The 

 space between the armatures and the dielectric was filled 

 with the lard-oil. Thus the fall of potential between the 

 armatures was uniform, and there was neither a free charoe 

 on the surface of the shellac tube nor any discontinuity in the 

 lines of force. The elongation due to the mechanical pressure 

 of the electrodes was eliminated, and according to the value 

 assumed for Poisson's ratio, a decrease of from one-fourth to 

 one-third of the deflexion for adherent armatures of the same 

 dimensions should result. Again, the distance between the 

 armatures is now increased to 7 millimetres, instead of the 

 former less amount. For number 7 it should reduce the 

 deflexion in the ratio of sixteen to forty-nine ; for number 9 

 of six and a quarter to forty- nine. 



The results actuallv obtained are given in the table. 



