TIIK ELECTRICAL EXPERIMENTS OF HENRY CAVENDISH. 



In the next part of his researches he investigates the capacities of con- 

 turned of plate* of different kinds of glass, rosin, wax, shellac, &c. 

 with di*k of tinfoil, and also of plates of air between two flat con- 

 ductor* He fioda that the electricity spreads on the surface of the plate 

 beyond the tinfoil coatings, and he investigates most carefully the extent of 

 thU spreading, and how it depends on the strength of the electrification. 



After correcting for the spreading, he finds that for coated plates of the 

 mmri mbctance the observed capacity is proportional to the computed capacity, 

 but it in always several times greater than the computed capacity, except in 

 the rttt 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 

 platea 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 " Itesults," 

 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 re- 

 sistance 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 diminution 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 

 aame 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 dif- 



