268 Prof. G. Quincke on the Capillary 



the particles of a liquid produce an increase in the density on 

 the surface of a liquid, and at the same time a tension on the 

 free surface where it is bounded by a vacuum. He has then 

 extended these considerations to the other surfaces of a liquid, 

 which are bounded by other liquids or solids, and has shown 

 that here also, for all points of tne same limiting surface, there 

 must be a constant tension, which, however, is smaller than at 

 the free surface of the liquid. 



On account of his extraordinary conciseness he is frequently 

 obscure ; and he has changed in the course of years ; for from 

 time to time he assigns the difference in the deportment of 

 various substances solely to their different density. 



But, from whatever point of view we start, we are always led 

 to the conclusion that the phenomena of capillarity must occur 

 not only with liquids but also with solids, provided they are not 

 absolutely rigid but permit a displacement of their smallest particles. 

 The author was originally led to this principle by the observation 

 that fused substances, such as cement or glass, which when soft 

 could form a surface of equilibrium, exhibit an unusual stability ; 

 and it seems in fact that a series of surprising phenomena may be 

 unconstrainedly explained by assuming a tension on the surface 

 of solids, whether they have a free surface (that is, bounded by 

 air), or a surface in common with some other solid or liquid. 



If the free surface of a solid is the same as that of a liquid 

 upon which the same external forces act, its free surface must 

 have a definite tenacity, measured by the pull exerted upon the 

 unit of surface. 



It must therefore be possible to express the tenacity of round 

 metal wires by two numbers, the first of which is proportional to 

 the section, and the second to the periphery of the wire. As the 

 author was about to make experiments as to the validity of this 

 law, his attention was drawn to a memoir by Karmarsch, which 

 appears but little known*. Karmarsch, by numerous experi- 

 ments on the tenacity of metal wires, arrived at exactly the same 

 law which the author, without knowing those experiments, had 

 deduced by theoretical calculations. 



Karmarsch expresses the tenacity of metal wires thus, 



F = dD 2 + Z>D; (1) 



where D is the diameter of the wire, and a and b are constants. 

 The validity of this expression has been demonstrated in wires of 

 gold, steel, iron, German silver, silver, brass, copper, platinum, 

 and zinc from the most various sources, and in both annealed and 

 unannealed condition. The difference between the observed 

 tenacities and those which can be calculated from the values 



* Mittheilungen dcs gew. Ver.filr Hannover, 1858, pp. 138-155. 



