b'88 



Prof. L. T. More on Dielectric 



and tooth. The position o£ the top plate of the frame was 

 regulated by the set screws at the top of the rods. The 

 dielectric exposed above the uppermost charged electrode was 

 made slightly less thick than that between the other electrodes, 

 and the space between the upper surface of the dielectric and 

 the top plate of the frame was filled with a thin layer of oil 

 of the same dielectric constant as the shellac mixture, and the 

 distance between the two electrodes was adjusted so that this 

 heterogeneous dielectric was electrically equivalent to that 

 between any other two of the electrodes. The ebonite tooth 

 was covered with insulating wax to prevent leakage or 

 sparking from the positively charged electrode. 



The method of measuring the deflexions was the same as 

 that employed in my former work, and the reader is referred 



I give here only 



Source x-! 



to those papers for a detailed description, 

 a brief account of it. 



The system of optical levers used 

 expansion of the condensers is shown in 

 descent electric lamp with a 

 ground glass globe was clamped 

 behind a metal screen pierced 

 with a round hole, five milli- 

 metres in diameter. Across 

 this opening fine platinum wires 

 were fastened horizontally, to 

 serve for the deflected image. 

 The light from the lamp, after 

 reflexion at right angles by a 

 totally reflecting prism, passed 

 through an achromatic lens to 

 a tilting mirror mounted ver- 

 tically on a little tripod table. 

 Upon reflexion, the light again 

 passed through the lens and on, 

 above the prism, to a micrometer 

 microscope. 



The mirror, 1*5 cm. X 2*0 cm., 

 furnished by Brashear, was 

 silvered on its front face and 

 plane to 1/4 \. The tilting 

 table of brass, 1*6 cm. square, 

 had three legs made of the finest 

 needle points, one of which 

 rested on the brass cylinder and 

 the other two on the ebonite tooth. 



to 



magnify the 

 4. An incan- 



Fiar. 4. 



* Image 



4-1 cm. 



Screen. 



4/cm,. 



k 



59cm 



37C77Z-. 



By slightly 



M//?R0f? 



raisins: or 



lowering the cylinder, the beam of light could be directed at a 



