[ 417 j 
XII. Measurements of Electrical Constants. —No. II. 
On the Specific Inductive Capacities of Certain Dielectrics* —Part I. 
By J. E. H. Gordon, B.A. Cantab, Assistant Secretary of the British Association. 
Communicated by Professor J. Clerk Maxwell, F.R.S. 
Received October 21,—Read December 12, 1878. 
Contents. 
Page. 
Introductory... 417 
Description of instruments employed— 
The coil... 418 
The wheel-break . 418 
The secondary reversing engine. ..'. 419 
The batteries .. 419 
The 5-plate induction balance. 420 
The mechanical slide . 422 
The Thomson electrometer. 422 
The callipers. 422 
Determination of speed of wheel-break. ..... 422 
Estimation of electromotive force of secondary 
current ... 423 
Page. 
Connections and general method of working 423 
The formula of calculation .. 427 
The experiments .. ... 428 
Table of results... 438 
Discussion of results and possible causes of 
error .. 439 
Measurement of the refractive indices of the 
transparent dielectrics. 440 
Results of the experiments on glass. 442 
Table comparing and ^/K . 444 
Conclusion, and suggestions for future 
work ... . ... 445 
Introductory. 
In the autumn of 1876 it was suggested in the course of a conversation with 
Professor Clerk Maxwell that I should, under his direction, undertake a series 
of measurements of specific inductive capacities—particularly those of transparent 
dielectrics—with a view of testing Professor Maxwell’s electro-magnetic theory of 
* A paper of mine with the above title was communicated to the Royal Society by Professor 
J. Clerk Maxwell, E.R.S., on March 9, 1878. It was read on Mai'ch 28, and an abstract of it was 
published in the ‘Proceedings of the Royal Society,’ vol. xxvii., p. 270. 
In the course of the summer it was pointed out to me that, owing to a mistake in the formula of 
calculation, all the results were wrong. 
I therefore requested permission to withdraw my paper, in order to recalculate the results. 
The new values of K arrived at led me to make some determinations of refractive indices, and to 
re-write the theoretical deductions at the end of the paper. 
I now beg, through Professor Maxwell, to present the paper in an amended form, with the hope that 
it may be found not entirely unworthy the attention of the Royal Society. 
MDOCCLXXIX. 3 H 
