286 THE POPULAR SCIENCE MONTHLY. 



perature, there are about nineteen million million million molecules. 

 All these numbers of the third rank are, I need not tell you, to be 

 regarded as at present conjectural. In order to warrant us in putting 

 any confidence in numbers obtained in this way, we should have to 

 compare together a greater number of independent data than we have 

 as yet obtained, and to show that they lead to consistent results. 



Thus far, we have been considering molecular science as an inquiry 

 into natural phenomena. But, though the professed aim of all scien- 

 tific work is to unravel the secrets of Nature, it has another effect, not 

 less valuable, on the mind of the worker. It leaves him in possession 

 of methods which nothing but scientific work could have led him to 

 invent, and it places him in a position from which many regions of 

 Nature, besides that which he has been studying, appear under a new 

 aspect. The study of molecules has developed a method of its own, 

 and it has also opened up new views of Nature. 



When Lucretius wishes us to form a mental representation of the 

 motion of atoms, he tells us to look at a sunbeam shining through a 

 darkened room (the same instrument of research by which Dr. Tyndall 

 makes visible to us the dust we breathe), and to observe the motes 

 which chase each other in all directions through it. This motion of 

 the visible motes, he tells us, is but a result of the far more compli- 

 cated motion of the invisible atoms which knock the motes about. In 

 his dream of Nature, as Tennyson tells us, he 



" saw the flaring atom-streams 

 And torrents of her myriad universe, 

 Eunning along the illimitable inane, 

 Fly on to clash together again, and make 

 Another and another frame of things 

 Forever." 



And it is no wonder that he should have attempted to burst the bonds 

 of Fate by making his atoms deviate from their courses at quite un- 

 certain times and places, thus attributing to them a kind of irrational 

 free-will, which on his materialistic theory is the only explanation of 

 that power of voluntary action of which we ourselves are conscious. 



As long as we have to deal with only two molecules, and have all 

 the data given us, we can calculate the result of their encounter ; but 

 when we have to deal with millions of molecules, each of which has 

 millions of encounters in a second, the complexity of the problem 

 seems to shut out all hope of a legitimate solution. 



The modern atomists have therefore adopted a method which is, I 

 believe, new in the department of mathematical physics, though it has 

 long been in use in the section of statistics. When the working mem- 

 bers of Section F get hold of a report of the census, or any other docu- 

 ment containing the numerical data of Economic and Social Science, 

 they begin by distributing the whole population into groups, according 

 to age, income-tax, education, religious belief, or criminal convictions. 



