692 



Prof. L. T. More on Dielectric 



These condensers were mounted in the same manner as the 

 glass ones in my earlier experiments. The values for Young's 

 modulus were obtained in the usual manner by placing 

 weights on the ends o£ the cylinders and measuring their 

 contraction. They are fairly accurate for the shellac, but the 

 value for the paraffin is not so reliable as the substance is 

 decidedly viscous. The values for both are given rather too 

 large than too small. 



Tube No. 7 was a little irregular in thickness, as it distorted 

 somewhat when taken from the mould. But the results are 

 of importance as they show the effect of a slightly non- 

 uniform field. Tube No. 9, after removal from the mould, 

 was turned in a lathe and was quite uniform in bore and 

 thickness. 



Tube 7. — Adherent Armatures. 



Spark- 

 length. 



Potential. 



Mean elong. 1 Mean elong. 

 micr. div. c^XlO 4 . 



Time of 

 charging. 



5'0 mm. 

 1 7-5 

 7o 



lo-o 

 iio-o 



10-0 



12-0 

 12-0 



60 c.g.s. 

 85 



85 



100 

 100 

 100 



110 

 110 



27-0 

 35-0 

 70-0 



55-0 

 100-0 



180-0 



133-5 

 242-5 



1-62 

 2-10 

 4-20 



3-30 



6-00 

 10-80 



8-01 

 14-55 



025 min. 



025 



1-00 



0-25 

 100 

 5-00 



0-25 

 1-00 



The elongations, 8/, are the mean in each case of a series 

 of readings. Since one division of the micrometer equals 

 6 x 10~ 6 mm., the absolute value of the deflexion is obtained 

 by multiplying the observation in divisions of the micrometer 

 by that number. 



In the first place, for the same time of charging the 

 elongation does not increase as the square of the potential. 

 Secondly, the dependence of the deflexion on the length of 

 time employed in charging is so pronounced as to make it 

 imperative to account for it by the heat evolved by the 

 electrical charge. When the condenser was discharged the 

 return of the image, as Cantone also noticed, is quite irregular; 

 at times the image returned quickly to the original zero, very 

 often about half way, but most often there was no recovery. 

 This is contrary to theory, as there should be no residual 

 effect of the charge. 



