376 



On Pendent Drops. 



[June 16, 



By weighing. 

 Diameter of tube "9525. Temperature 4° C. 



Calculated. 



T 1= -07598 

 T 2 = -07685 

 T,= -07930 



Observed. 



•07516 

 •07797 

 •07897 



c=- -03030 

 T= -07180 



It will be observed that the values of T for water vary very con- 

 siderably. Moreover, on no occasion have I obtained so high a value 

 as the mean "08253 deduced by Professor Quincke by the method of 

 flat bubbles. 



The agreement of the measures is in each case so close as to leave no 

 doubt that the surface tension of the liquid really differed con- 

 siderably on different occasions. I have at present no better explana- 

 tion of this to offer than the fact that the surface tension of water is 

 particularly liable to diminution by exposure to the impurities of the 

 atmosphere. 



To aid a comparison of the method with that of flat drops or 

 hubbies, on which Professor Quincke seems chiefly to rely, I append 

 a table giving the values of the tensions by the two methods in 

 parallel columns. It is to be observed that the liquids used are often 

 not quite the same, as is indicated by the difference of density. 



The name of the observer is signified by the initial letter. 



Name of substance. 



Density. 



Surface tension in grams 

 per centim. 



Q. 



W. 



Q. 



W. 





l 



•7906 

 •8867 

 •9136 

 ] -4878 



1 



•8001 

 •8679 

 •92129 

 1 5129 



•08253 

 02599 

 •03030 

 03760 

 •03120 



•0718 to -08005 

 •02586 

 •028179 

 03373 

 •03025 



Professor Quincke's result in the case of water is the mean of seven 

 measures ranging between "0800 and *0892 ; that for turpentine is 

 the mean of eight ranging from "0284 to '0318 ; that for olive oil is 

 the mean of seven, ranging from '03617 to *04113. 



The method of flat drops and bubbles is, as he himself points out, 

 only approximate, since the curvature due to revolution is neglected, 

 and is liable to give results that are rather too high. 



