184 3Ir. G, Johnstom Stonetj [Fob. 6, 



Primary and Secondary Motions. 



This will be a convenient place in wliicli to draw attention to a 

 distinction of importance in the study of nature : the radical distinction 

 which exists between primary motions and secondary. Secondary 

 motion exists wherever there is a transference from place to place of 

 other underlying motions. Primary motions are those that have no 

 other more subtile motions underlying them. None of the senses 

 with which man is furnished, even when aided to the utmost by the 

 microscope, have ever reached primary motions, nor have they indeed 

 been able to penetrate beyond coarse forms of secondary motion ; and 

 it should be observed that the science of dynamics deals exclusively 

 with this class of motions. 



When the spore of a mushroom is hurried along by the wind, the 

 vast accumulation of molecular motions that are going on within its 

 small volume is being drifted forwards, and constitutes the visible 

 motion of the spore a secondary motion. In what enormous numbers 

 underlying motions are here present may be judged from considering 

 that comx^lex motions go on within every chemical atom, that there 

 are within the most minute organic spec that has ever been seen with 

 a microscope enough of chemical atoms to make up from 10,000 to 

 100,000 of the most comj^lex organic molecules known to chemists, 

 allowing thousands of chemical atoms for each of these complex 

 molecules, and that a vast number of such organic specs would be 

 needed to make up a very tiny spore. It will thus be perceived that 

 the motions that go on within a spore are in inconceivable numbers 

 and of extraordinary complexity. The motion of a spore, then, when 

 drifted by the wind is a rather coarse secondary motion, i. e. it is? 

 the travelling forwards of a complicated mass of underlying motions. 



A far less coarse motion is taking place in the molecules of gas 

 as they dash about among each other in the way described above. 

 Yet here again the motion is secondary, for within each molecule 

 there are the motions going on that originate the lines seen with 

 the spectroscope. Whether these internal motions are primary or 

 secondary we do not yet know, but the probability seems to be that 

 even they are secondary and that underlying them there are still 

 more subtile motions. There is in fact some reason to susj^ect that 

 chemical atoms may be likened to the vortex rings of which an im- 

 perfect illustration is shown in the beautiful experiment in which 

 smoke rings are shot across a room. Two or more chemical atoms 

 unite to form a molecule of the gas. The advance of the vortex ring- 

 across the room will stand for the travelling motion wdiicli carries an 

 atom of the gas along as part of its molecule, the pulsation which is 

 often seen passing round the vortex ring may represent the heat and 

 light vibrations wliicli take place within each atom of the molecule, 

 and underlying both of these is the vortex motion itself, which may 

 perhaps correspond to the real primary motion in the molecule. 

 However, in the present state of science wc do not know certainly 



