164 Dr. W. F. Magie on the 



of much smaller bubbles. That this assumption is not admis- 

 sible can be seen at once, from a computation of the correction- 

 term involving the semidiameter of the bubble in the formula 

 for a 2 which is given by Poisson, and presented later in this 

 paper. It will be found that, for a bubble of the diameter of 

 100 millim., the correction to be applied to reduce the value 

 of a 2 obtained on the assumption made by Prof. Quincke, 

 amounts for water to more than 5 per cent., for alcohol to 

 nearly 3 per cent., and for other liquids to similar percentages 

 of their respective values of a 2 . Further, the application of 

 such a correction, or indeed of Poisson's formula, as used by 

 Prof. Quincke in his study of the capillary constants of mer- 

 cury"*, to bubbles of which the diameters are rarely greater 

 than 30 millim., is at least questionable t- In no case does 

 the application of Poisson's formula to the measurements 

 given by Prof. Quincke reduce the values of a 2 , which in the 

 first approximation are too great, to an agreement with the 

 results obtained from similar measurements of large bubbles, 

 to which the application of Poisson's formula is, without 

 doubt, admissible. 



Dr. Traube presents, as evidence of the existence of a finite 

 acute contact-angle and of its variability with temperature, 

 his measurements of the heights of the meniscus in capillary 

 tubes J. This height was always less than the radius of the 

 tube, and diminished as the temperature rose. Similar results 

 were obtained by MM. Haiiy and Tremery§, and by Dr. Schiff || . 

 With regard to the results of MM. Haiiy and Tr^mery, 

 Laplace showed that a slight error in determining the point 

 of contact of the liquid surface with the tube would account 

 for the discrepancy observed, and he concludes that the expe- 

 riment offers no proof of a finite contact-angle. The experi- 

 ments of Dr. Traube are open to a serious objection. The 

 diameters of the tubes employed were so great, that not only 

 is the first approximation, which Dr. Traube adopts, that, in 

 case the contact-angle is zero, the surface of the meniscus is 

 a hemisphere, and the height of the meniscus equal to the 

 radius of the tube, entirely inadmissible, but even the closer 

 approximation, given by Poisson % cannot be legitimately 

 applied, except possibly in the one case of water. This ap- 

 proximation is based upon the assumption that the radius of 

 the capillary tube is very small compared with the capillary 



* Quincke, Pogg. Ann. cv. p. 1 (1858). 



t Magie, Wied. Ann. xxv. p. 434 (1885). 



% Traube, Jour, fur prak. Chem. xxxi. p. 514 (1885). 



§ Laplace, Mec. Cel. vol. iv., Suppl. to 10th Book, p. 63. 



|| Ann. Chem. Phar. ccxxiii. p. 49. 



H Nouv. Th. de t Act. Cap. p. 110. 



