308 Mr. W. Sutherland on the 



his rich experimental material, published in the Annalen der 

 Chemie, vol. ccxxiii., and in Wiedemann's Beihldtter, vol. ix. 

 (from the Mem. delta JR. Ace. d. Lincei, 1884), combined with 

 Eotvos' law, will be used to determine the parameter A ; it 

 is therefore necessary briefly to take note of a discussion 

 which has been raised over a certain assumption of Schiflf's. 

 He assumes that the angle of contact of liquid with glass is 

 zero in every case in his determinations; but at the same time, 

 in order to take account of the weight of the meniscus in his 

 determination of surface-tension, he gives measurements of 

 the distance between the top and the bottom of the meniscus, 

 as this distance is in many cases different from the radius of 

 the tube. The meniscus surface would appear to be different 

 from the hemisphere, which it ought very approximately to 

 be if the contact-angle were zero. Volkmann pointed out this 

 (^Annalen der Chemie, vol. ccxxviii.), and recalculated the 

 capillary constants from SchifF's determinations on the assump- 

 tion that the data for the height of meniscus might be used 

 for determining the angle of contact which he introduces into 

 the calculation for the surface-tension. These recalculations, 

 while they take away from the definiteness of some of SchifF's 

 minor results, do not affect the truth of his broad discovery. 

 There is no doubt that, on theoretical grounds, Volkmann's 

 criticism is sound enough ; that the experimental data, as 

 furnished, bore evidence to the existence of a finite contact- 

 angle not taken into account in the calculations. But it must 

 be remembered that the measurements of the heights of the me- 

 niscus were undertaken only for use in a small correction ; and 

 that such measurements are not competent to give satisfactory 

 evidence of a finite contact-angle, and are certainly not com- 

 petent to give a measure of it. The manner in which the 

 apparent height of the meniscus vai'ies in SchifF's data with 

 temperature shows in a practical manner the unreliability of 

 such measurements for testing the difficult question of contact- 

 angle. SchifF admits the theoretical justness of Volkmann's 

 criticism as to contact-angle, but appeals to the regularity of 

 his own results as his practical justification. As Volkmann 

 himself has shown (and Quincke also) that the contact-angle 

 for a large number of watery solutions of inorganic salts is 

 zero, and as ordinary meniscus measurements would not de- 

 monstrate the fact, we are on the whole safe in assuming with 

 SchifF that all his liquids wet glass (that is, that their contact- 

 angle is zero), until the point is settled by a satisfactory 

 experimental method. 



In applying the law of the inverse fourth power to the ca- 

 pillary theory we cannot use directly the formulae already 



