668 Messrs. Narayan and Subrahmanyam on Surface 

 where of course e is the eccentricity defined by 



*> 7 9 



a" — b z 



i * f i i 2C i ■ 



a 2 









*(*- 



' X) * 



4C 2 



' 2 4 





2 



\ ■ 





2V2 



-D(i- 



- 2 > ,« 



6(\ 





3! 





' r 



+ 



...J, 



which in the present case, as e is smaller than I, is a rapidly 

 converging series and can be calculated to the desired degree 

 of approximation. 



Some readings have, however, been taken with a few 

 capillary tubes having very nearly a circular bore. In the 

 case of such tubes, correction for the weight of the liquid 

 above the bottom of the meniscus in the capillary tube is 

 applied according to Hagen & Desain's formula 



A=M-. T a 



oa' + r 



where a 2 is the capillary constant, h and h are observed and 

 corrected heights. 



The height of the liquid column and the diameter of the 

 tube are measured in all these cases by a comparator (reading 

 to hundredths of a mm.), for which we are indebted to the 

 C.S.I. Co., England. The following observations (Tables 

 III. to Y.) are the mean of a number of readings, which, 

 from considerations of space, we could not give in detail. 

 Before each set of measurements the tubes are thoroughlv 

 cleaned by a hot mixture of nitric and chromic acids and 

 washed well in plenty of running tap-water, and finally dried 

 in a current of warm air. 



(In preparing the solutions, excess of soap is at first taken, 

 and is dissolved in water. The solution is then allowed to 

 settle, and the clear liquid decanted into a beaker. It is then 

 filtered twice. One hundred c.c. of this filtered solution is 

 successively diluted with 100, 200, 300, 400 ? .... c.c. of water. 

 Hence the concentrations are expressed in terms of the 

 saturated solution.) 



It will be seen that the surface tension in all these cases 

 never differs much from 23*5 dynes per cm. (Temp. 29°'l C), 

 and is about the same as Lord Riyleigh\s results, whose 

 values range between 25*3 and 24*6 dynes per cm. (Temp. 

 18°) (" On the tension of water surfaces, clean and con- 

 taminated, investigated by the method of ripples" (Phil. Mag. 

 xxx. pp. 386-400, November 1890). ' 



