248 



ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1910. 



the limits .0013 cm. per sec. and .47 cm. per sec. Complete records 

 of a few of these observations are given in Tables IX, X, XI, and 

 XII. 



[The reader may consult these tables in the original article, but 

 they are here necessarily omitted for lack of space.] 



The readings shown in these tables are merely samples of the 

 sort of observations which we took on between 100 and 200 drops 

 between December, 1909, and May, 1910. The sort of consistency 

 which we attained after we had learned how to control the evapora- 

 tion of the drops and after we had eliminated dust from the air 

 may be seen from Table XIII which contains the final results of 





fOO 1000 . IS'QQ 2000 



ZSoo 3000 



jfoo- WW ^foo Sooo 



Fig. 2. 



our observations upon all of the drops except three which were 

 studied throughout a period of 47 consecutive days. The three drops 

 which have been excluded all yielded values of e x from 2 to 4 per 

 cent too low to fall upon a smooth e 1 v 1 curve like that shown in 

 figure 2 which is the graph of the results contained in Table XIII. 

 It is probable that these three drops corresponded not to single drops, 

 but to two drops stuck together. Since we have never in all our 

 study observed a drop which gave a value of e x appreciably above 

 the curve of figure 2, the hypothesis of binary drops to account for 

 an occasional low value of e x is at least natural. Before we elimi- 

 nated dust we found many drops showing these low values of e x , 

 but after we had eliminated it we found not more than one drop in 



