NEW PLUMS AND PRUNES 155 



the radiation of radium) the mass of an atom is 

 so inconceivably small that the number of atoms 

 making up a portion of matter as big as our 

 plum bud (which we may assume to have the 

 bulk of about a cubic centimeter) is represented 

 by the figures 68 followed by twenty- four 

 ciphers 68 "octillions," if the figures must be 

 read. 



So the number of atoms that are aggregated 

 in the tiny plum bud is vastly greater than the 

 total number of people that have lived on the 

 earth since the human race was evolved. 



To attempt to give tangibility to the idea of 

 the smallness of the atom, we may borrow an 

 estimate made by the late Lord Kelvin. It may 

 be computed that if the tiny plum bud were 

 imagined to be enlarged in size until it became 

 as big as the earth, each component atom being 

 increased in the same proportion, its entire struc- 

 ture would then be made up of units (magnified 

 atoms) of about the size of footballs. 



If we then reflect, further, that according to 

 the definite analyses of other physicists, with Sir 

 J. J. Thomson of Cambridge at their head, each 

 atom is itself a complex structure the very sim- 

 plest atom, that of hydrogen, being composed of 

 at least 1,700 particles called electrons which are 

 in reality the unit particles of electricity we 



