SECT. XIV. COHESION. 101 



The phenomena arising from the force of cohesion 

 are innumerable. The spherical form of rain drops ; 

 the difficulty of detaching a plate of glass from the sur- 

 face of water ; the force with which two plane surfaces 

 adhere when pressed together; the drops that cling to 

 the window-glass in'a shower of rain are all effects of 

 cohesion entirely independent of atmospheric pressure, 

 and are included in the same analytical formula (N. 

 158) which expresses all the circumstances accurately, 

 although the laws according to which the forces of 

 cohesion and repulsion vary are unknown. It is more 

 than probable that the spherical form of the sun and 

 planets is due to the force of cohesion, as they have 

 every appearance of having been at one period in a state 

 of fusion. 



A very remarkable instance of cohesion has occasion- 

 ally been observed hi piate-glass manufactories. After 

 the large plates of glass of which the mirrors are to be 

 made have received their last polish, they are carefully 

 wiped and laid on their edges with their surfaces resting 

 on one another. In the course of time the cohesion 

 has sometimes been so powerful, that they could not be 

 separated without breaking. - Instances have occurred 

 where two or three have been so perfectly united, that 

 they have been cut and their edges polished as if they 

 had been fused together, and so great was the force 

 required to make their surfaces slide that one tore off a 

 portion of the surface of the other. 



The size of the ultimate particles of matter must be 

 small in the extreme. Organized beings possessing life 

 and all its functions, have been discovered so small that 

 a million of them would occupy less space than a grain 

 of sand. The malleability of gold, the perfume of 

 musk, the odor of flowers, and many other instances 

 might be given of the excessive minuteness of the 

 atoms of matter ; yet from a variety of circumstances it 

 may be inferred that matter is not infinitely divisible. 

 Dr. Wollaston has shown that in all probability the 

 atmospheres of the sun and planets as well as of the 

 earth consist of ultimate atoms no longer divisible ; and 

 if so, that our atmosphere only extends to that point 

 where the terrestrial attraction is balanced by the elas- 



