﻿474 M. G. Quincke on the Capillary Phenomena 



expected a change of the constant Kj, and consequently a de- 

 crease of the elevation. As was pointed out at the commence- 

 ment of this memoir, /. c, no strict inference can be drawn re- 

 garding the magnitude of the perpendicular pressure K in the 

 free plane surface of a liquid, as 



K x — K 2 may be =K 12 =— K 21 . 



This relation, however, according to the numbers of Table X. 

 § 10, which never give ei n = u x — 0L 2i is very improbable; and 

 on this account I am disposed to agree with the opinion of 

 Thomas Young, according to which K 1? the perpendicular pres- 

 sure in a plane surface of a liquid, is to be put =0. 

 Berlin, September 1869. 



The foregoing memoir was already written, when, by the kind- 

 ness of the author, I received the very interesting treatise of M. 

 G. van der Mensbrugghe " On the Surface-tension of Liquids"*. 

 It treats of motions on the free surface of liquids exhibited by 

 other liquids, particles of camphor, or small solid bodies ; and, 

 from the same points of view as myself, he seeks the cause of 

 these phenomena in the different magnitudes of the capillary 

 tension of the surface of the liquid, which can be materially 

 modified through the solution of small quantities of foreign 

 substances. The greater or less tension of the free surface of 

 the liquid is proved by a method discovered by the author, from 

 the change in shape of the closed curves which are formed of 

 thin threads swimming on the surface of the liquids. The 

 treatise also contains a complete literature of the earlier works 

 on the same subject. 



As we proceeded in quite different ways independently of one 

 another in the investigation of the same phenomena, I believed 

 it was unnecessary to alter any thing in my written statement, so 

 much the more so as, in my opinion, a complete understanding 

 of the process of outspreading cannot be obtained without a 

 knowledge of the magnitude of the capillary constant of the 

 common surface of two liquids. Moreover all the experiments 

 described by M. van der Mensbrugghe are in harmony with the 

 foregoing theoretical considerations. 



The principal results of the foregoing investigation may be 

 recapitulated as follows : — 



1. At the common boundary of two liquids 1 and 2 a similar 

 tension of surface takes place to that on the free surface of a liquid 

 bounded by air. 



* G. van der Mensbrugghe " Sur la tension superficielle des liquides," 

 M£m. Cour. et d. Sav. Strang, d. Brnx. vol. xxxiv. pp. 1 to 67, 4to. See 

 also p. 409 of Phil. Mag. for December, 1869. 



