10 FEAGMENTS OF SCIENCE. 



the atoms to cross the minute spaces which separate 

 them amounting only to an inconceivably small fraction 

 of a second. 



It has been stated that when a body falls to the 

 earth it is warmed by the shock. Here, to use the ter- 

 minology of Mayer, we have a mechanical combination 

 of the earth and the body. Let us suffer the falling 

 body and the earth to dwindle in imagination to the 

 size of atoms, and for the attraction of gravity let us 

 substitute that of chemical affinity; we have then what 

 is called a chemical combination. The effect of the 

 union in this case also is the development of heat, and 

 from the amount of heat generated we can infer the 

 intensity of the atomic pulL Measured by ordinary 

 mechanical standards this is enormous. Mix eight 

 pounds of oxygen with one of hydrogen, and pass a 

 spark through the mixture; the gases instantly com- 

 bine, their atoms rushing over the little distances which 

 separate them. Take a weight of 47,000 pounds to an 

 elevation of 1,000 feet above the earth's surface, and let 

 it fall; the energy with which it will strike the earth 

 will not exceed that of the eight pounds of oxygen 

 atoms, as they dash against one pound of hydrogen 

 atoms to form water. 



It is sometimes stated that gravity is distinguished 

 from all other forces by the fact of its resisting conver- 

 sion into other forms of force. Chemical affinity, it is 

 said, can be converted into heat and light, and these 

 again into magnetism and electricity: but gravity re- 

 fuses to be so converted; being a force maintaining 

 itself under all circumstances, and not capable of dis- 

 appearing to give place to another. The statement 

 arises from vagueness of thought. If by it be meant 

 that a particle of matter can never be deprived of its 

 weight, the assertion is correct; but the law which af- 



