MATTER 17 



sodium wave of light, which would be something 

 more than Yioojooo of a centimetre in thickness. But 

 the molecules of this thin film are very complex, so 

 that in the thickness of the film quite a number of 

 atoms must exist. 



Sir William Thomson says "that in any ordinary 

 liquid, transparent solid, or seemingly opaque solid, 

 the mean distance between the centres of contiguous 

 molecules "is less than the Vs, 000,000 and greater than 

 the Vi'Ooo,ooo,ooo of a centimetre."* 



" To form some conception of the degree of coarse- 

 grainedness indicated by this conclusion, imagine a 

 globe of water or glass, as large as a football, to be 

 magnified up to the size of the earth, each constituent 

 molecule being magnified in the same proportion. 

 The magnified structure would be more coarse-grained 

 than a heap of small shot, but probably less coarse- 

 grained than a heap of footballs." 



It is said that the smallest object visible under 

 the microscope is x /4,ooo of a millimetre, which is about 

 Vioojooo of an inch, and yet such an object contains 

 millions of molecules. It has been claimed that an 

 organic being of that size would contain perhaps one 

 million molecules of organic matter in addition to the 

 water which constitutes most of its bulk. 



Crookes, taking the estimate that 1 c. c. of air con- 

 tains 1,000,000,000,000,000,000,000 molecules, says that 

 to fill a globe 13.5 centimetres in diameter, which has 

 been exhausted to the one-millionth of an atmosphere, 

 would require, if the molecules entered at the rate of 

 100,000,000 in a second, 408,501,731 years. At the 

 above rate it would require about 2,500,000 years to 

 fill a globe one inch in diameter. If we estimate the 

 number of molecules at 19,000,000,000,000,000,000 in 

 a cubic centimetre, as has been done by some, then 



*Popular Lectures and Addresses, Sir W. Thomson, p. 217. 



