302 



S. Ii. Williams — Electromagnetic Effect. 



the mercury column in one of the side tubes, and the field 

 strength when the direction of the field was changed.* At 

 first the results were very erratic. This was found to be due 

 largely to the adhesion of the mercury to the walls of the tube. 

 This trouble was remedied by placing a small quantity of 

 glycerine on top of each meniscus. The glycerine behaved as 



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FIG. 8 



a lubricant and the mercury moved along the tube like a well- 

 oiled piston. With the glycerine covering all of the exposed 

 mercury surfaces, the tubes could be left for weeks and would 

 still yield consistent results. As a precaution the tubes were 

 tilted in various directions each time they were used in order 

 to get the glycerine down around the edges of the meniscus. 

 The elevation and depression of the mercury column was read 

 by means of a microscope and micrometer eyepiece in the case 

 of tubes 1, 2, and 3, while a telescope and micrometer eyepiece 

 were used for tubes 1 and 5. 



Discussion of Results. 



From the curves 1, 2, 3, and 4 it would appear that the 

 smaller the tubes the more the mercury was displaced. Curve 

 5, however, contradicts this, and all of the curves point to the 



* Fifteen amperes flowed through the vertical central column of mercury 

 for all the values given. 



