18 Experimental Philosophy . [Lecture 2. 



Fir 



Beech 



Oak 



Pear, 



Lemon 



The direct cohesive strength of a body is in 

 the joint ratio of its primitive elasticity, of its 

 toughness, and the magnitude of its section. 



Cohesion is also visible even in fluid substances, 

 the particles of which adhere together, though 

 with a less degree of tenacity than solid bodies. 

 " The pearly dew*" is a well known phrase in 

 poetical language, and the drops of rain or of 

 dew upon the leaves of plants assume this round 

 or pearly appearance by the attraction which the 

 particles have for one another. In the same 

 manner quicksilver, if divided into the smallest 

 grains, will appear round, like small shot, because 

 the particles attract each other equally in every 

 direction, and thus each particle draws others to 

 it on every side as far as its power extends. For 

 the same reason two small drops of quicksilver, 

 when brought near to each other, will seem to 

 run together and unite. 



The attraction of cohesion exists between fluid 

 and solid bodies. Thus a plate of glass or metal 

 (Plate I. fig. 1.) which has been immersed in 

 water or mercury, will retain some drops hanging 

 to it, even when turned upside down, or inverted. 

 Again, if two plates of glass, A. A. (fig. 2.), a 

 little wetted on the surface, and separated on one 



