•] -Measurements ofSpecifid Inductive Capacity of Dielectrics. 285 



Hence 



p s -nu?+xu fa 



| „ — = ccos#,r; 



.*. putting #=0, 



1 « 2 + M 2 

 a7 -co 



Integrating this equation, and choosing the arbitrary constant so that c 

 may vanish when n is infinite, 



. J: Jn ^» 



Hence we shall have 



1 rr~ 2 — — 2 V 7r cos awe" 2 " 1 «/i e-«V 2 , 



which last integral is exceedingly well known. It is manifest that we can 

 reduce the integral I — 2? . , 2r to this by the method of partial 



J_QO a U 



fractions. 



In concluding this paper, I desire to express the obligations I am under 

 to Spitzer's ■ Studien.' 



II. "Measurements of Specific Inductive Capacity of Dielectrics, 

 in the Physical Laboratory, of the University of Glasgow." By 

 John C. Gibson, M.A., and Thomas Barclay, M.A. Com- 

 municated by Sir William Thomson. Received November 

 23, 1870. 



(Abstract.) 



This paper describes the instruments and processes employed in a series 

 of experiments on the specific inductive capacity of paraffine, and the 

 effect upon it of variations of temperature. The instruments described are 

 the platymeter and the sliding condenser. The former of these was, in a 

 rudimentary form, shown to the Mathematical and Physical Section of the 

 British Association at its Glasgow Meeting in 1855, by W. Thomson. It 

 consists of two equal and similar condensers employed for the comparison of 

 electrostatic capacities. The sliding condenser is a condenser the capacity 

 of which may be varied by known quantities by altering the effective area 

 of the opposed surfaces. By means of these two instruments, along with 

 the quadrant electrometer, the capacity of a condenser may be determined 

 by equalizing the sliding condenser to it. The method of working, and 

 the electrical actions upon which it depends, are described in detail. In 



