Stoney — Appreciation of Ultra- Visible Quantities. 539 



of the marvellous precision of this, the latest and most searching 

 appliance for exploring nature. By it a brilliant series of dis- 

 coveries have already been made in stellar astronomy ; and we 

 may anticipate still greater achievements from the distance to 

 which it can throw its plumb-line into the obscure depths of 

 molecular events. 



X. — Time Relations. 



The fragments of time that can be appreciated with accuracy 

 in this way are even more wonderful in their minuteness than are 

 the differences of length. Time relations, however, lie somewhat 

 outside the scope of the present essay ; but they, too, should be 

 carefully pondered by anyone who wants to know what Nature 

 really is. And after thus taking the best survey that he can, he 

 should bear in mind that all he can do is to gauge the little that 

 man has been fortunate enough to detect ; and that far more may 

 lie beyond the ken of any human being than the immense range 

 which now lies within it. He should also reflect that the few 

 molecular events that are already known succeed one another with 

 such astonishing rapidity that the swiftest visible motions are, in 

 relation to them, as sluggish and as gradual in their progress as 

 are the changes in the configurations of the constellations owing 

 to the proper motions of the fixed stars, in their relation to us and 

 to the events we can see occurring about us on the earth. In fact, 

 the thousandth of one second of time is, in relation to them, compar- 

 able with some such period as twenty or thirty thousand years in 

 its relation to man's "slow thoughts, or the drif tings about of those 

 accumulations of molecules which are the only kind of objects 

 he can perceive even with the highest powers of his microscope. 

 • These visible objects, these armies of molecules massed together, 

 seem to him sometimes at rest and sometimes in motion ; but in 

 either case strenuous activity within and between the molecules 

 themselves never ceases, nor the perpetual response between them 

 and the aether through which they keep up a communication with 

 one another at a distance. The magnitude of the consequences 

 throughout all nature of this unflagging intercourse between 

 molecules cannot be approached by the utmost thought we can 

 give to it. It is quite impossible for us to appreciate it ade- 

 quately. The human eye placed anywhere intercepts a small 



