100 C. Barus — Bepulsion of Ttvo Metallic Disks. 



as, for instance, in case of series 1 and 4. The evidence, how- 

 ever, is none the less definite. In series 1 and 3, 5 and 6, 7 

 and 9, the equilibrium position is approached from opposite 

 directions. 



To obtain some reason for this result, one may dismiss the 

 effect of electrical repulsion at once. The experiments to be 

 made in the next section are for the purpose of corroborating 

 the force equation used. Furthermore, friction at the pivots 

 may be excluded, since the pendulum is usually in motion, 



Fig. 4. 



</0 



OS 



04 



oz 



00 



02 



1 









i 













A 







\ 





t 







its 



> \ 

















;f 





i yl 



75 10 



■65 



\l 



i 







e-- 



15 \ 



Is 







U,JM5 



V l 



p 





5 

 A-15 



ns 









m f 



iO 













0™ 20 40 60 Z0 40 60 W 40 



swinging about its position of equilibrium, so that friction 

 would have operated both ways. There remains the possibility 

 of an excess of pressure in the couche of air within a metallic 

 fissure as compared with the surrounding air. To obtain some 

 quantitative data, since B' B = 65*2Ai^, one may note that in 

 the successive series of measurements the average values of 

 2AJV were roughly as follows : 



Fig. 4 



Earlier 



experiments 



do. 



2AiY"X 10 3 = 40 



2Ai\^X 10 3 = 13, 22, 38 

 2AiV r X 10 3 = 40 



Max. F' R = 1-3 dynes 



Min. F\ 



As the area of the disk is 324 sq. cm., the corresponding aver- 

 age pressure observed per cm. is therefore here 



p = 4 X 10 -3 dynes /cm 2 = 4 X 10~ 9 atm., 



