216 JONES-STRONG— THE ABSORPTION SPECTRA [April 24. 



This is largely owing to the almost infinite complexity of the struc- 

 ture of the atom and our general ignorance of the forces that exist 

 there. Probably the best known example is that of the uranyl 

 group which we have been describing. Let us consider the spectral 

 vibrations that can be produced by components that exist or may 

 be produced from the apparently simple UOo group : ( i ) We have 

 the absorption spectrum described above. At low temperatures 

 most of these bands break up into much finer bands. (2) The 

 uranyl salts under various methods of excitation emit a phosphor- 

 escent spectrum of a large number of rather fine bands throughout 

 the visible region of the spectrum. It is quite possible that this 

 spectrum is intimately connected with that of the absorption spec- 

 trum. (3) We have the absorption spectrum of the uranous salts 

 which has been described above. This spectrum has been probably 

 caused by the change of valency of the uranium atom. Uranium 

 is known to form quite a large number of oxides and it is quite 

 possible that for each valency of the uranium we have a character- 

 istic spectrum. (This also is being investigated.) It is also quite 

 probable that at low temperatures those spectra would consist of 

 quite fine bands. (4) We have the spark spectrum and the ab- 

 sorption spectrum of oxygen, and (5) that of ozone, which bears 

 no relation to that of oxygen. (6) There is the exceedingly com- 

 plex spark spectrum of uranium consisting of thousands of fine 

 lines and also (7) the complex arc spectra. From radioactive ex- 

 periments it is known that uranium is continually breaking down into 

 ionium. (8) Ionium possesses the properties of a chemical atom 

 and most likely has a spectrum of its own. This would make 

 eight spectra. (9) Ionium breaks down into the radium and radium 

 has a very characteristic spark spectrum, as does also (10) the 

 radium emanation. During the various radioactive transforma- 

 tions several a products are emitted with a velocity almost as 

 great as that of light. It is probable that these particles are mov- 

 ing with very great velocities in the uranium atom under ordinary 

 conditions. (11) The a particles are known to be charged helium 

 atoms and therefore under proper excitation would give the helium 

 spectrum. The radium emanation breaks down into Radium A, 

 B, C, D, E and F. These products behave like chemical elements 



