422 OF CAPILLARY ATTRACTION AND THE COHESION OF FLUIDS. 



It is also by the principles of capillary attraction, that the lymph 

 and other fluids are taken up, and transferred through the ramifying 

 vessels to every part of the animal frame ; other causes dependent on 

 the organical structure both of plants and animals, may assist in 

 producing this effect ; but it is abundantly proved by observations, 

 that by far the greatest part of it is produced by capillary attraction 

 alone. It is solely owing to it, that a piece of dry wood absorbs a 

 considerable quantity of moisture, and in consequence of this absorp- 

 tion it swells with a force almost irresistible, thereby splitting rocks 

 and other bodies of inconceivable hardness and tenacity. 



Consequently, since the principles of capillary attraction are found 

 to exercise such extensive influence in the operations of nature, philo- 

 sophers are justified in attempting to acquire a more precise and 

 comprehensive knowledge of the manner in which it acts, and of the 

 laws by which that action is regulated during the period of its opera- 

 tion on natural bodies. 



526. DEFINITION. Capillary Attraction is that principle in nature, 

 by which water and other liquids are made to ascend in slender tubes, 

 to heights considerably above the level of the fluid in the containing 

 vessel ; it is so called, because its influence is only sensible in tubes 

 whose bore is extremely small, in general very little exceeding the 

 diameter of a hair, but never greater than one tenth of an inch. The 

 tube thus limited, and in which the fluid is found to ascend, is called 

 a capillary tube, from the Latin word capillus, a hair. The principles 

 of capillary attraction, and the theory which it unfolds, together 

 with its application to tubes of various forms and diameters, we shall 

 very briefly consider in the present chapter ; the chief and most im- 

 portant properties peculiar to this subject are detailed in the following 

 experiments. 



527. EXPERIMENT 1. There is an attraction of cohesion between the 

 constituent particles of glass and water. 



This is manifest, for if a very smooth plate of glass be brought into 

 contact with water, and then gently removed from it, it will be found 

 that a small portion of the fluid adheres to the glass, and remains 

 suspended from the lower surface when placed in a horizontal posi- 

 tion ; hence the existence of an attraction is inferred, and its intensity 

 must be such, as to balance and sustain the gravitating power of the 

 water. 



And again, if a smooth plate of glass be suspended horizontally 

 from one arm of a lever, and kept in equilibrio by a weight applied 

 at the other arm ; then, if the glass be brought into contact with the 



