ATOMS AND MOLECULES 27 



contains, suppose, 30 cubic inches of gas. In each cubic 

 inch are 10 23 molecules, and therefore altogether 30 x 10 23 . 

 A jar of hydrogen of the same size, and under the same 

 conditions, will also contain 30 x 10 23 . One of nitrogen, 

 chlorine, or any gas, will have the same number ; or the 

 same jar will contain just the same number of each. It 

 is the same number of molecules, not of atoms. The 

 number of the latter differs in the molecules, and there- 

 fore also in the jar. What determines the number? 

 There are the action of the molecules on each other, the 

 same heat energies and pressure of the atmosphere. 

 And though the molecules involved be so great in 

 number, the heat motions so multitudinous, and the 

 atmospheric pressure produced by so lofty an atmosphere, 

 so perfect are their constitution and action that they 

 everywhere and always, in the case of every gas, put the 

 same number of molecules into the same space. Were 

 the space increased to cubic yards or miles, they would 

 still be equal to the task. So perfect is the constitution 

 of molecules, and the action of all natural laws on them, 

 that they can put enormous numbers into the same 

 spaces, and always the same. If a shepherd had ten 

 thousand sheep, and wanted to put them in hundreds 

 into pens, each one having a measured space around it, in 

 which it might move freely, as have the molecules, he could 

 not accomplish such a task without careful counting and 

 measuring. And nature could not accomplish it without 

 the vastest amount of measuring going before. And so, 

 although it may be said that it is natural to gases to 

 obey these laws, we cannot but ask, Why is it natural ? 

 The simplest and most natural results that are, have 

 great meanings. They speak of order. They could not 

 be produced without it, without a great amount of it, and 

 of the finest kind. There cannot be a single law without 



