88 Prof. Clerh Maxwell, On unpublished experiments. [Nov. 5, 



than the computed capacity, except in the case of plates of air, 

 Cavendish thus anticipated Faraday in the discovery of the 

 specific inductive capacity of dielectrics, and in the measurement 

 of this quantity for different substances. 



For these experiments Cavendish constructed a large number 

 of coated plates with capacities so arranged that by combining 

 them he could measure the capacity of any conductor from a 

 sphere 12'1 inches diameter to his large battery of 49 Leyden 

 jars. He expressed the capacity of any conductor in what he 

 calls " inches of electricity," that is to say the diameter of a sphere 

 of equal capacity expressed in inches. 



The details and dates of the experiments referred to in this 

 work are contained in three volumes of experiments in the* years 

 1771, 1772 and 1773, in a separate collection of "Measurements" 

 and in a paper entitled "Results," in which the experiments of 

 different days are compared together. Besides these there are 

 experiments of other kinds which are not described in the 

 treatise. 



The most important of these experiments are those on the 

 electric resistance of different substances, which were continued 

 to the year 1781. 



He compares the resistance of solutions of sea salt of various 

 strengths from saturation to 1 in 20000, and measures the diminu- 

 tion of resistance as the temperature rises. He also compares the 

 resistance of solutions of sea salt with that of solutions containing 

 chemical equivalents of other salts in the same quantity of water. 

 He finds the resistance of distilled water to be very great, and 

 much greater for fresh distilled water than for distilled water 

 kept for some time in a glass bottle. 



I have compared Cavendish's results with those recently 

 obtained by Kohlrausch, and find them all within 10 per cent. 

 and many much nearer. 



Cavendish also investigates the relation between the resistance 

 and the velocity of the current, and finds the power of the velocity 

 to be by different experiments 1-08, I'OS, 0-976 and 1, and 

 he finally concludes that the resistance is as the first power of 

 the velocity, thus anticipating Ohm's Law. 



The general accuracy of these results is the more remarkable 

 when we consider the method by which they were obtained, forty 

 years before the invention of the galvanometer. 



Every comparison of two resistances was made by Cavendish 

 by connecting one end of each resistance-tube with the external 

 coatings of a set of equally charged Leyden jars and touching the 

 jars in succession with a piece of metal held in one hand, while 

 with a piece of metal in the other hand he touched alternately the 

 ends of the two resistances. He thus compared the sensation of 



