the Surface Tension of Liquids. 191 



plate supported by three porcelain rests in a glass dish. The 

 dish stood upon a low table furnished with levelling screws. 

 The liquid to be investigated filled the dish above the lower 

 surface of the plate, but did not cover the upper surface. With 

 this arrangement it was possible to obtain bubbles over 10 cm 

 in diameter of almost perfectly circular section, and by careful 

 manipulation of the levelling screws to bring the bubbles 

 momentarily to rest under the middle of the plate. 



When the bubble was formed and had become as nearly sta- 

 tionary as possible, the microscope was brought over its center, 

 and* lowered until it was sharply focussed on the image of the 

 paper reflected from the approximately plane surface of the 

 bubble. The position was then read on the cathetometer scale, 

 and the microscope raised by means of the tangent screw of 

 the cathetometer, until it was focussed on the image of the 

 paper reflected from the lower surface of the glass plate. The 

 position was again read on the cathetometer scale. It can easily 

 be shown that the difference of these two position-readings was 

 equal to the height of the bubble. The scale of the cathetom- 

 eter could be read directly by means of a vernier to twentieths 

 of a millimeter. 



The diameter of the bubble, which only enters in the correc- 

 tion term, was measured with sufficient exactness with an ordi- 

 nary millimeter scale. 



The results which I have obtained by the use of this method 

 compare very favorably for uniformity with those given by any 

 other method. They are presented in the following tables, in 

 order to show what may be expected of the method. They are 

 not, however, to be taken as final results. 



The values for Jc and I are given in millimeters, and a 2 is 

 given instead of a, as it is the constant usually employed. 





Distilled Water. 





k 



1 



a 2 



Temp. 



5-60 



56 



15-093 



22° a 



5'56 



56 



14-962 



22 



5-59 



63-5 



15-179 



19 



5'57 



63-5 



15-070 



19 



5-57 



57 



Mean, 



15-031 



19 





15-067 





5'65 



53 



15-398 



6 



5-605 



55 



15-179 



6 



5-634 



52-5 



15-311 



6 



5-64 



55 



15-367 



7 



Mean, 15-314 



