1889.] Electrolytes to very rapidly alternating Current*. 287 



primary, stopping and starting the coils several times ; if, during this 

 time, no sparks passed in the secondary, the sparks were considered 

 stopped. A variation of 5 per cent, in the quantity of electrolyte 

 present would cause the system to pass this point one way or another 

 in a marked way. 



The balls at the extremity of the secondary were adjusted so that 

 sparks passed freely before the electrolyte was put in, after each ex- 

 periment the electrolyte was removed, and care was taken to ascertain 

 that sparks still passed as freely as before so as to guard against any 

 accidental disarrangement of the secondary during the experiment. 



Three sets of coils were used which we shall describe by I, II, III. 

 Set I consisted of two- circular brass coils, 140*8 c. in circumference. 

 The diameter of the brass rod of which they were made was about 

 0"6 c. ; the balls at the extremities were 2 c. in diameter. The time 

 of vibration of this coil, calculated by equation (18), is about 10~ 8 

 seconds. 



Set II consisted of two circular copper coils 81*2 c. in circumference, 

 the rod of which they were made being about 0'5 c. in diameter; the 

 balls at the extremities were 1 c. in diameter. The time of vibration 

 is about 5 X 10~ 9 seconds. With these small coils the balls of the 

 secondary had to be exceedingly close together in order to get sparks, 

 but when the micrometer screw was properly adjusted the sparks were 

 very bright and the indications quite definite. The coils were about 

 9 c. apart. 



Set III consisted of two rectangular coils made of sheet lead, one 

 side was 30 c., the other 40, the breadth of the sides was 5 c., and 

 the diameter of the balls at the extremity 2. The distance between 

 the coils was 15 c. The time of vibration about 10~~ 8 seconds. 



The electrolytes used were solutions of 



In the following table the relative thickness of the films of these 

 substances required to stop the spark is given, each number being the 

 mean of several observations. The thickness of the H 2 S0 4 film was 

 taken as unity. An observation with sulphuric acid was made before 

 and after the observation with any other electrolyte. 



