156 Mr. J. E. H. Gordon on Electrical Constants. [Dec. 12, 



Results. 



Dielectric. 

 Glass, Slabs about 1 inch 

 thick. 



{Double extra dense flint 3 

 Extra dense flint 3 

 Light flint 3 

 Hard crown 3 



3 -2581 

 3 -2282 

 2 -2697~| 

 2 -2482 I 

 2 -3097 f 

 2 -3077 J 



Common 

 2 



11 \ 

 $2/ 



plate, f No. 1 

 I No. 2 

 rNo. 1 



Ebonite, 4 slabs, J No. 2 

 f, 1 1 i inch. 1 No. 3 

 iNo. 4 



Best quality gutta percha 2 



Chatterton's compound 2 



india-rubber < , . -, rt 

 [ vulcanised 2 



Solid paraffin, sp. 



K. 



1639 

 •0536 

 •0129 

 •1079 



3 -2431 



2 -2838 



•4625 

 •5474 

 •2200 

 4969 



gr.atll°O.'9109. 1 



No. 1 



1 -9940 



Melting point 



No. 2 



1 -9784 



68° C. 6 slabs cut < 



No. 3 



1 -9969 



in planing ma- 



No. 4 



2 -0126 



chine. Results 



No. 5 



1 -9654 



corrected for ca- 



No. 6 



2 -0143 



I Mean. ..1-9936* 



vities. x / 



Shellac 2 7464 



Sulphur 2-5793 



Bisulphide of carbon 1 *8096f 



The following table compares the refractive indices of the transpa- 

 rent dielectrics with the square roots of the specific inductive capacities. 

 In cases where there is a wide difference /x is taken from books on 

 physics ; wherever there was a close agreement it was carefully deter- 

 mined by the author, except in the case of paraffin, where the value is 

 that given in Maxwell's " Electricity." 



* Messrs. Gibson and Barclay, " Phil. Trans.," 1871, using a method entirely 

 different from mine, obtained K = 1*977 for paraffin. Correcting for a slight difference 

 of density, I find that if they had used my paraffin their result would haye been 

 1-9833. 



f I am not quite certain of the accuracy of this result. 



