OF ARTS AND SCIENCES. 



223 



cathetometer. In this way, it was found possible to get the plates 

 sensil)ly parallel. The poles of the induction coil were connected with 

 a condenser ; one directly, and the other by means of the spark passing 

 between the two discs. The condenser was then discharged through 

 a galvanometer. The micrometer screw of the cathetometer reads 

 easily to the yo'^^,^ of a millimetre, and observations were taken with 

 its aid at intervals of .050 mm. The plates were considered to be in 

 contact, whenever making the primary circuit gave any deflection in 

 the galvanometer. The zero thus obtained was quite constant, where- 

 as it was almost imj^ossible to tell by the eye just at what point the 

 spark ceased to pass when the circuit was broken. The poles of the 

 battery were kept apart when not actually in use, and it was supposed 

 that the electro-motive force remained constant durino; the time of ob- 

 servation. 



In laying out a curve, it must be remembered that there was a 

 resistance of 6000 ohms already in the circuit. ICach of the following 

 results i? the mean of a series of closely agreeing observations : — 



