142 



"WELLS'S NATURAL PHILOSOPHY. 



SECTION I 



Explain the 

 phenomena ob- 

 Berved when 

 the hand is 

 l^hmged into 

 different liq- 

 uids. 



CAPILLARY ATTRACTION. 



321. If we plunge the hand into a vessel of water, and 

 withdraw it, it is said to be wet ; that is, it is covered with a 

 thin film, or coating of water, which adheres to it, in opposi- 

 tion to the tendency of the attraction of gravitation to mako 

 it fall off. There is, therefore, an attraction between the par- 

 ticles of the water and the hand, which, to a certain extent, 

 is stronger than the influence of gravitation. 



If now we plunge the hand into a vessel of quicksilver, no adhesion of the 

 particles of the mercury to the hand will take place, and the hand, when 

 withdrawn, will be perfectly dry. 



If we plunge a plate of gold, however, into water and quicksilver, it will 

 be wet equally by both, and will come out of the quicksilver covered with a 

 white coating of that liquid. 



It is, therefore, obvious that a certain molecular attraction exists between 

 certain liquids and certain solids, which does not prevail to the same extent 

 between others. 



322. That variety of molecular force which 

 manife.sts itself ] jet ween the surfaces of solids 

 and liquids is called Capillary Attraction, 



This name oiigiuatcs from the circumstance, that this class 



of phenomena was first observed in small glass tubes, the 



bore of which was not thicker than a hair, and which were 



hence called Capillary Tubes, from the Latin word ca])illus, which signifies a hair. 



„ „ 323. If we take a series of glass tubes of very fine bore, 



How may Ca- ° 



piUary Attrac- but of different diametei-s, and place them m a vessel oi water, 



tion bo illuB- -wiiich has been colored in order to show the effect more strik- 

 trated ? 



ingly, we shall see that the water will rise in the tubes to 



various heights, attaining the greatest degree of elevation in the smallest tube. 



What 18 Ca- 

 pillary Attrac- 

 tion? 



What is the 

 origin of the 

 term ? 



FlO. 128. 



The height at which the same Uquid will rise in 

 any given tube is always uniform, but it varies for 

 different liquids. 



Pig. 123 is an enlarged representation of tho 

 manner in wliich water will rise in tubes of diQer- 

 ent diameters. 



The simplest method of exhibiting capillary at- 

 traction is to immerse the end of a piece of ther. 

 moraeter tube in water (see Fig. 12D) which has 

 been tinted with ink. The liquid will be seen to 

 ascend, and will remain elevated in the tube at a 

 considerable height above the surface of the liquid 

 in the vessel 

 The ordinary definition of capillary attraction ia, that form of attraction which 



