104 



CAPILLAEY ELEVATIONS AND DEPRESSIONS. 



Fig. ST. 



Capillary among physical writers as CAPILLARY ATTRACTION. Its nature 

 attraction. may -fo e illustrated as follows : 



If a piece of glass be laid on the surface of quicksilver, it is so power- 

 fully attracted thereto as to require the exertion of considerable force to 

 lift it off. Natural philosophers generally regard this as a force sui ge- 

 neris, and speak of it under the title of capillary attraction. I believe it 

 is nothing but an ordinary electrical phenomenon, since, if the glass be 

 examined, it will be found to be in a positively electrified state, and the 

 quicksilver negative, and under the general law of electricity, known as 

 that of Dufay, attraction must be the result. 



If the glass be laid upon the surface of water, there is 

 an attraction as before. On lifting it, however, there is 

 no electrical manifestation; The reason of this is plain. 

 On examining this glass, it will be found that no true 

 separation of it from the water has taken place. A film 

 of water is still attached to it, or, in other words, it is 

 wetted. 



If a slender glass tube, , Fig. 37,be dippedinto a liquid, 

 Elevation and a, a, which can not wet it, as, for example, 

 ilqSlrca^. quicksilver, the liquid is depressed as at c, 

 maiy tubes, and does not rise to its proper hydrostatic Depression of a non . 

 level, or, perhaps, altogether refuses to enter the tube. wetting liquid. 



Fig. ss. If a slender glass tube, b, Fig. 38, be dipped into 



a liquid, , #, which can wet it, as, for example, water, 

 the liquid at once rises in the tube, as at c, to a height 

 which is greater in proportion as the diameter of the 

 tube is less. It is this phenomenon which has given 

 the designation capillary attraction, because it is 

 best seen in tubes as fine as a hair (capillus). 



Now if there be a tube of such a diameter that it 

 could thus lift water ten inches, and it be broken off 

 so as to be only six inches long, we might inquire 

 whether the water would overflow from its top, or 

 simply remain suspended. 

 Mathematical considerations as well as direct experiments prove that, 

 in such a case, there would be no overflow. A capillary tube under 

 these circumstances simply lifts the water, but can not produce a contin- 

 uous current. 



But if a removal of the water at the top of the tube takes place in any 

 Conditions for manner as > f r instance, by evaporation, or by being dissolved 

 producing a away, then a continuous current is produced. This fact ex- 

 plains the phenomena of endosmosis, presently to be de- 

 scribed. 



Elevation of a wetting 

 liquid. 



