136 Mr. A. Ferguson on the Shape of the 



Approximately a 2 = B; and therefore, more exactly. 



a 2 = B + f^JL, .... (xxvi.) 

 12v/B' 



a very convenient equation from which to calculate a 2 . 



The elementary theory which assumes the bubble to be 

 hemispherical gives 



« 2 =iWi-p' /l ') (xxvii.) 



An idea o£ the relative importance of these correcting 

 terms will best be obtained from the consideration of the 

 results of an experiment made upon ethyl alcohol, using a 

 capillary tube slightly less than a millimetre in diameter 

 (such a tube is about the widest that can be safely employed). 

 Using water in the manometer, the heights hi and 1i were 

 measured by means of a travelling microscope. The follow- 

 ing figures were obtained: — 



Temp. = 12°-5 0. 

 ] h = 5-072 cm., h' --= 5-059 cm. 



pi=l gm. per c.c, p'= *795 gm. per c.c. 

 r= -04595 cm. 

 Erom which equation (xxvii.) gives 



a 2 = -03038 sq. cm., or T = 23*69 dynes per cm. 

 The first approximation a 2 = B gives 



a 2 = -02964 sq. cm., or T=23*12 dynes per cm. 



The final approximation embodied in equation (xxvi.) gives 

 a 2 = -02972 sq. cm., or T = 23'18 dynes per cm. 



The final figures are in good agreement with the result 

 obtained by the writer by a totally different method * — the 

 measurement of the mechanical pull on a sphere of large 

 radius "just touching the liquid surface. This gave T 15 = 23'll 

 dynes per cm. 



§8. The formulae of §§ 1-4 may be used also in discussing 

 certain aspects of the classical experiments of Ramsay and 

 Shields f on the molecular complexity of liquids. In these 



* Phil. Mag. Nov. 1913, p. 925. 

 t Phil. Trans. A. 1893, p. 647. 



