214 LECTURES. 



(105.) The equilibrinru of the capillary forces may be expressed by 

 the followincr general equation in which Z is the elevation or depres- 

 sion, T a co-efficient for each fluid and solid, R and W the radii of 

 curvature 



^=^(i+-y (^^•) 



(106.) Illustrations of the effects of curvature on the length of the 

 column — the exterior surface of a liquid rendered concave, the column 

 in the tube depressed — convex the reverse. The surface of the exterior 

 liquid made concave, the height of the column in the tube diminished — 

 convex increased. 



Column supported in a tube with a drop of liquid at the end is de- 

 pressed by touching the drop to a surface of liquid — effect of convex 

 and concave surface exhibited by means of a small inverted syphon. 



Movement of a drop of water in a conical glass tube — also between 

 two glass plates. 



Reverse movement of a drop of mercury. 



Apparent attraction of two plates with film of water interposed. 

 Effect of double curvature of the liquid surface, 



A small glass rod in a large capillary tube filled with water, does 

 not fall out but rebounds from the lower surface of the liquid. 



Illustration of Copillai-y Fhenomena. — Surface crystallization — water 

 imbibed by sponge, the pores require to be previously wetted by pres- 

 sure. Water drawn up into sand. Oil supplied by the wick — bundle 

 of fine wire may be used for the same purpose. Method of oiling the 

 axles of the locomotive. Marble absorbs oil but not water ; the oil 

 extracted by clay. 



Water passed through filtering paper by capillary force, collects on 

 the lower side into drops^ by cohesion, falls by gravity. Different 

 liquids separated by previously wetting the filter with one of them. 

 Cloth rendered air-tight by water. 



The dimensions of bodies are often changed by imbibing water. 

 The untwisting of catgut, and of the beard of the wild oat, the short- 

 ening of strings and the lengthening of whalebone, all fu nish hi/gro- 

 scopes, or instruments for indicating the state of moisture of the air. 



The intensity of the capillary action is exceedingly great ; water is 

 drawn into wood with such force as to split rocks. A large weight 

 raised by the contraction of a rope in the direction of its length, while 

 it is increasing in diameter. The same force is not exerted when oil 

 is absorbed. Cause of warping and splitting of furniture — use of oil- 

 ing and varnishing to prevent this. 



French method of saturating timber with substances for its preser- 

 vation. 



(107.) Apparent attraction and repulsion of floating bodies. — Two 

 moistened or two smoked corks approach each other; but a moistened 

 and a smoked cork separate. Also a moistened cork adheres to the 

 side of a glass vessel, partially filled with water, but it moves towards 

 the centre when the liquid is heaped on the vessel above the rim. 



(108.) Endosmose, (from evSov and (oa/jto^). The transmission of 



