80 PROCEEDINGS OF THE AMERICAN ACADEMY 



In series 2 the uormal pressure was slightly less than in the other-?. 

 The excessively high value of 40 X 10~^ at which in series 5 good 

 quality still persisted, is the highest that has been observed. The 

 hammer electrode had been brought to a sharp point just previously. 



I have observed, among the four persons who have employed the 

 method under consideration, that each one has apparently his own 

 standard of what constitutes good quality, and usually adheres quite 

 closely to this in different experiments. The observer last cited gen- 

 erally gave somewhat larger values to the excursion for a given degree 

 of excellence of transmission than I noted in my own observations, 

 apparently from this cause. 



A further series of measurements was made in order to ascertain 

 what effect was produced by a variation in the normal pressure be- 

 tween the electrodes. 



In order to do this, a wire was caused to project backward from the 

 anvil electrode, and small weights were hung upon the end of it. The 

 pendulum electrode with this projecting wire constituted a bent lever 

 whose arms were easily measured, thus enabling the normal pressure 

 due to a given weight to be calculated. It was thus obtained very 

 easily, although the method is subject to the objection that there is a 

 certain variation of the mass of the anvil electrode simultaneously with 

 the variation in pressure. The use of a delicate spring instead of the 

 weight would be preferable, but I have not yet found time to carry 

 through observations by this method. The results reached are shown 

 in Tables XVII. to XIX. 



TABLE XVII. 



Electrodes, Platinum, Platinum. 



Normal Pressure in Grams. Excursion of Hammer at Critical Point. 



0.34 8 X 10-6 



0.77 14 X 10-6 



1.20 25 X 10-6 



1.63 37 X 10-6 



2.06 50 X 10-6 



2.50 61 X 10-6 



0.34 10 X 10-6 



0.77 12 X 10-6 



1.20 25 X 10-6 



1.63 37 X 10-« 



2.06 50 X 10-6 



2.50 61 X 10-6 



2.98 61 X 10-6 



