46 SCIENCE AND IMMORTALITY 



molecule on the point of a needle would be like a 

 midge on the summit of the Matterhorn ; and 

 that the molecules in a tear would exceed the 

 population of the world. 



All these illustrations are interesting ; but the 

 most imaginative picture of the smallness of mole- 

 cules we know is that given by Sir William Crookes 

 in his essay on Radiant Matter. He points out 

 that a vacuum bulb (the glass bulb used in the pro- 

 duction of X-rays) holds a quadrillion molecules, 

 and that even when apparently exhausted it still 

 contains a trillion. What trillion and quadrillion 

 mean he explains : " To suggest some idea of this 

 vast number, I take the exhausted bulb and perfor- 

 ate it by a spark from the induction coil. The 

 spark produces a hole of microscopic fineness, yet 

 sufficient to allow molecules to penetrate and to 

 destroy the vacuum. The inrush of air impinges 

 against the vanes and sets them rotating after the 

 manner of a windmill. Let us suppose the mole- 

 cules to be of such a size that at every second of 

 time a hundred millions could enter. How long, 

 think you, would it take for this small vessel to 

 get full of air ? An hour ? A day ? A year } 

 A century ? Nay, almost an eternity ! A time so 

 enormous that imagination itself cannot grasp the 

 reality. Supposing this glass bulb, indued with 

 indestructibility, had been pierced at the birth of 



