1% Prof. Millikan and Mr. Winchester on Influence of 



the following method was adopted and found to work 

 admirably. 



The small room in which the work was done was kept as 

 dry as possible with trays of sulphuric acid and calcium 

 chloride, and a current of thoroughly dried air was kept 

 blowing against the electrode E or E\ which was connected 

 to the electrometer. The persistence with which moisture 

 adheres to a glass surface is shown by the fact that it required 

 three or four days of continuous blowing to obtain an elec- 

 trode dry enough for our purpose. The success attained in 

 the end, however, is shown by the fact that with a deflexion 

 of 25 cm. the leak was not more than *1 mm. in five minutes. 

 Since the following observations never required more than 

 two or three minutes at most, it will be seen that the natural 

 leak was completely eliminated. At temperatures above 

 .100° C, however, another source of leak appeared, for which 

 it was necessary to make a correction in the manner indi- 

 cated below. 



In the series of observations which follows, the wheel was 

 joined to one pair of quadrants of the electrometer and to 

 this system was connected the negative pole of a battery 

 of 20 cells (one volt each), the positive pole being joined 

 to earth. The other pair of quadrants and the gauze g 

 were also connected to earth. The deflexion was observed. 

 then the connexion between the battery and electrometer 

 was broken. The leak being inappreciable, the deflexion 

 remained constant. At an accurately noted instant the 

 induction-coil was started and the light allowed to fall on the 

 disk under examination for exactly 10 seconds, as measured 

 by a stop-watch. After an interval of about 50 seconds, the 

 electrometer having again come completely to rest, the 

 reading was taken. The difference between the two readings 

 represented the discharge due to the light. 



At temperatures above 100° C, a leak similar to that 

 observed with the aluminium electrode at 340° C. (cf. § 4) 

 began to make its appearance. A correction for this leak 

 was made in the manner indicated in the description of the 

 earlier experiments for aluminium. The readings in Table II. 

 for the temperatures 100° C. and 125° C. are therefore 

 weighted with somewhat larger errors than are those taken 

 at temperatures below 100° C. At 150° C. this leak — clue to 

 increased temperature — had become so large that the correc- 

 tion could not be made with certainty, while at 180° C. the 

 needle swung back to zero about as quickly when the light 

 was off as when it was on. 



That this leak due to the increase in temperature became 



