152 SOME OF THE LATEST ACHIEVEMENTS OF SCIENCE. 



sensitized photographic lihiis capabh^ of dealing- with the necessary 

 small amount of radiation given by feebly phosphorescing substances/ 

 and, above all. tireless patience in collating and interpreting results, 

 have all played their part. Although the research is incomplete, I 

 am able to announce that among the groups of rare earths giving 

 phosphorescent spectra in the visible region there are others giving 

 well-defined groups of bands which can only be recorded photograph- 

 ically. I have detected and mapped no less than six such groups, 

 extending to X 3060. 



Without enlarging on difficulties. 1 will give a brief outline of the 

 investigation. Starting with a large quantity of a group of the rare 

 earths in a state of considerable purity, a particular method of frac- 

 tionation is applied, splitting the earths into a series of fractions dif- 

 fering but slightly from each other. Each of these fractions, phos- 

 phorescing in vacuo, is arranged in the spectrograph, and a record of 

 its spectrum photographed upon a specially prepared sensiti^^e film. 



In this way, with different groups of rare earths, the several invis- 

 ible bands were recorded — some moderately strong, others exceedingly 

 faint. Selecting a portion giving a definite set of l)ands, new methods 

 of fractionation were applied, constantly photographing and measur- 

 ing the spectrum of each fraction. Sometimes many weeks of hard 

 experiment failed to produce an}' separation, and then a new method 

 of splitting up was devised and applied. By unremitting work — the 

 solvent of most difficulties — eventually it was possible to split up the 

 series of bands into vai'ious groups. Then, taking a group which 

 seemed to ofi^er possibilities of reasonably quick result, one method 

 after another of chemical attack was adopted, with the ultimate result 

 of freeing the group from its accompanying fellows and increasing 

 its intensit}' and detail. 



As I have said, m}^ researches are far from complete, but about one 

 of the bodies I may speak definitely. High up iji the ultra-violet, like 

 a faint nebula in the distant heavens, a group of lines was detected, at 

 first feeble, and only remarkable on account of their isolation. On 

 further purification these lines grew stronger. Their great refrangi- 

 bilit}' cut them ofl^ from other groups. Special processes were employed 

 to isolate the earth, and using these lines as a test, and appealing at 

 every step to the spectrograph, it was pleasant to see how each week 

 the group stood out stronger and stronger, while the other lines of 

 yttrium, samarium, ytterbium, etc., became fainter, and, at last, 

 practically vanishing, left the sought-for group strong and solitary. 

 Finally, within the last few weeks, hopefulness has emerged into cer- 



^ In this connection I am glad to acknowledge my indebtedness to Dr. Schumann, 

 of Leipzig, for valuable suggestions and detail of his own apparatus, by means of 

 which he has produced some unique records of metallic and gaseous spectra of lines 

 of short wave-length. 



