308 Mr. J. Brown. [Nov. 1 8, 



ampere current, or to a circuit consisting of a Leclanche cell and an 

 ordinary astatic galvanoscope. A telephone was also generally 

 included in the circuits. When joined up with the cell in circuit it 

 was possible by very careful adjustment of the distance between the 

 plates to find a point where although they were not in metallic 

 contact still a current would pjass. The needles of the galvanoscope 

 (which flew to the stops when the plates were in actual contact) were 

 deflected unsteadily to about the same extent as if the condenser 

 were replaced by a resistance of 50 to 100 ohms, and a faint hissing 

 sound was heard in the telephone. If now the terminals from the 

 plates were transferred to the galvanometer, a current was observed 

 varying in different experiments according to circumstances from a 

 few up to 130 divisions, but which at once ceased when the plates 

 were either placed in metallic contact or so far apart as to separate 

 the films on them. 



31. Measurements of the thickness of the two films were made by 

 the micrometer screw at M. Its indications are, however, only 

 approximate, since the upper plate does not remain parallel to the 

 lower while being raised ; and also (the whole apparatus not being 

 very rigid) it is quite possible that when the upper film rested on the 

 lower one, there was sufficient pressure on the surface of the plates to 

 prevent the upper one falling to the extent indicated by the micro- 

 meter readings, although a weight of six pounds was placed on the 

 end of the upper board at A to help to depress it. I give, however, a 

 series of readings typical of those obtained in all the experiments. 



M denotes the reading on micrometer corresponding to the distance 

 through which it rose in thousandths of an inch. D is the deflection 

 on galvanometer. (The adjustment for great sensitiveness rendered 

 its zero unstable.) 



Hygrometric state of air measured by B-egnault's form of hygro- 

 meter was 0*77. 



M= 0-5 07 1 15 2 2-5 3 35 4 4'5 4 

 D = 10 90 70 90 70 55 40 40 25 10 10 



Rates in contact. Films apart. 



M= 35 3 25 2 15 1 05 

 D = 35 38 40 50 50 50 15 5 



^ 



Plates in contact. 



Hygrometric state of air= 0*655— 



M= 1 15 2 25 3 35 3 25 2 15 

 D = 30 65 68 75 65 40 32 32 58 67 35 



Plates in contact. Films apart. 



The plates were very carefully dusted before use with a camel- 

 hair brush, and it was necessary also to avoid breathing on them, as 



