472 Dr. Gr. Johnstone Stoney : Survey of that part of 



reaction ? The incidents of the operations that are then 

 going on are vastly more numerous, are probably as various, 

 and are done with as little hurry when we view them from 

 the molecular standpoint, as are the acts of human artizans or 

 of other animals while accomplishing some piece of work ; 

 and they are, relatively speaking, persisted in for an almost 

 immeasurably longer time, inasmuch as the fifth of a thousandth 

 of a second in the molecular world corresponds to something 

 like 1900 years in ours. 



An estimate of this kind is of service, because it leads us to 

 see that biological and chemical processes, even where they 

 seem to us to take place with suddenness, are from the mole- 

 cular standpoint protracted events consisting of individual 

 transactions, each of which can only occur when the oppor- 

 tunity presents itself : they are not the outcome of the 

 ordinary current of molecular events, but, on the contrary, 

 each step of progress in them may have to wait long for some 

 very exceptional combination of circumstances to arise. The 

 present writer once saw doublets thrown thirteen times in 

 succession with unloaded dice, at the close of one game of 

 backgammon and at the beginning of the next game. It 

 must be an unusual experience for a human being to be 

 witness to so rare an event. The probability of it is only one 

 in 13,060, 700,000. Yet so great is the number of molecules 

 in a gas, and so frequent their encounters, that some millions 

 of cases occur every second hi every cubic micron of the air 

 about us, in which an encounter between molecules has taken 

 place under conditions as exceptional as the above ; and 

 equally unusual events probably occur some thousands of 

 times more frequently in the encounters between the mole- 

 cules of two liquids, or of a liquid and a solid. It is thus 

 that chemical reactions and events in biology can extend over 

 a duration which is appreciable by us, even in the case of 

 explosions ; the fact being that in all such events it is their 

 excessive slowness from the molecular standpoint that has to 

 be accounted for. On the other hand, the frequency when 

 estimated from the human standpoint of events which are 

 excessively rare when viewed from the molecular standpoint, 

 has enabled all the constituents of an atmosphere to escape 

 from the moon in the time which has elapsed since the moon 

 became separated from the earth ; and occasions such a leaking 

 away from the upper regions of the earth's atmosphere of 

 hydrogen and helium, the atmosphere's lightest constituents, 

 as would become appreciable within a few millions of years 

 were it not that these gases are being continuously filtered 

 into the atmosphere from beneath. 



