Septembeb 30, 1910] 



SCIENCE 



445 



TABLE X 



Negative drop No. 29 

 Distance between cross hairs ^ 1.007 cm. 

 Temperature =21.8°C. 



v=:.2l75 



Mean e^ = 5.046 



F's mean (? = 4.629. M's mean G = 4.632. 



Deferences 



Cn 



«1 



196.12 — 191.11= 5.01 -Hi = 5.01 

 226.21 — 196.12 = 30.09 -H 6 = 5.02 

 226.21 — 201.30 = 24.1 1 -f- 5 = 4.98 

 206.59 — 186.39 = 20.20 -H 4 = 5.04 



error 

 1 per cent. 



1 per cent. 



2 per cent. 

 1 per cent. 



201.69 — 186.39 = 15.30 H- 3 = 5.10 1 per cent. 



Mean difiference (weighted) =5.035. 



the bottoms of the tables. In fact, in general, 

 even with the largest drops the relative value'' 

 of e, can be determined with an accuracy of .5 

 per cent, from the differences alone. The ac- 

 curacy is, of course, increased by dividing the 

 values of e„ by n as soon as n has been found 

 with certainty from the differences. 



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 evaporation 

 of the drops, and after we had eliminated dust 

 from the air, may be seen from table XII., 

 which contains the final results of our obser- 

 vations upon all of the drops except three 



° Since the same value of G is used in computing 

 all of the e„% the relative values of e„ or e^ are 

 practically independent of the error in G. 



