x PEEFACE. 



of calcium and so forth, in their laboratories, and have com- 

 pared the bright lines visible in the spectra with the dark 

 ones in the stars, and on this ground they have announced 

 the discovery of calcium in the sun or of hydrogen in 

 Sirius. 



In all this work they have taken for granted that in the 

 spectrum thus produced in their laboratories, they have been 

 dealing with the vibration of one specific thing, call it atom, 

 molecule, or what you will ; that the vibrations of these 

 specific molecules have produced all the lines visible, which they 

 have persistently seen and mapped in each instance. 



Now, it was not long before my work raised the question 

 whether what has been thus taken for granted is really true. 

 And now that the question is raised, the striking thing about 

 it is that it was not asked long ago. 



Time out of mind or, rather, ever since Nicolas le Fevre, 

 who was sent over here by the French king at the request of 

 our English one at the time the Royal Society was established, 

 pointed out that chemistry was the art of separations as 

 well as of transmutations it has been recognised that with 

 every increase of temperature, or dissociating power, bodies 

 were separated from each other. In this way Priestley, from 

 his " plomb rouge " separated oxygen, and Davy from potass 

 separated potassium ; and as a final result of the labour of 

 generations of chemists, the millionfold chemical complexity 

 of natural bodies in the three kingdoms of nature has been 

 reduced by separations till only some seventy so-called elements 

 are left. 



Now this magnificent simplification has been brought about 



