234? DISCOURSE ON THE STUDY 



sition from one extreme to the other; and that, 

 however strongly marked the distinctions between 

 them may appear, they will ultimately turn out to 

 be separated by no sudden or violent line of de- 

 marcation, but shade into each other by insensible 

 gradations. The late experiments of Baron Cagnard 

 de la Tour may be regarded as a first step towards 

 the full demonstration of this (199.). But the 

 cohesion of liquids is not, like that of solids, so 

 modified by their structure in other respects as to 

 destroy the mobility of their parts one among an- 

 other (unless in those cases of nearer approach to 

 the solid state which obtain in viscid or gummy 

 liquids). On the contrary, the two qualities co-exist, 

 and give rise to a number of curious and intricate 

 phenomena. 



(253.) One of the most remarkable of these is 

 capillary attraction, or capillarity as it is sometimes 

 called. Every body has remarked the adhesion of 

 water to glass. The elevation of the general surface 

 of the liquid where it is in contact with the con- 

 taining vessel ; the form of a drop suspended at the 

 under side of a solid : these are instances of capil- 

 lary attraction. If a small glass tube with a bore 

 as fine as a hair be immersed in water, the water 

 will be observed to rise in it to a certain height, 

 and to assume a concave surface at its upper ex- 

 tremity. The attraction of the glass on the water, 

 and the cohesion of the parts of the water to each 

 other, are no doubt the joint causes of this curious 

 effect ; but the mode of action is at once obscure 

 and complex ; and although the researches of La- 

 place and Young have thrown great light on it, fur- 



