28 REPORT— 1898. 



their secrets, and were duly embalmed in the riiUosophical Transactions. 

 At the Birmingham meeting of the British Association in 188G I brought 

 the subject before the Chemical Section, of which I had the honour to be 

 President. The results led to many speculations on the probable origin 

 of all the elementary bodies — speculations that for the moment I must 

 waive in favour of exj^erimental facts. 



There still remained for spectroscopic examination a long tempting 

 stretch of unknown ultra-violet light, of which the exploration gave me no 

 rest. But I will not now enter into details of the quest of unknown lines. 

 Large quartz prisms, lenses, and condensers, specially sensitised photo- 

 graphic iilms capable of dealing with the necessary small amount of radia- 

 tion 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 gi'oups of rare earths giving phosphorescent spectra in the visible 

 region there are others giving well defined groups of bands whicli can only 

 be recorded photographically. I have detected and mapped no less than 

 six such groups extending to \ 3060. 



Without enlarging on difficulties, I will give a brief outline of tlie in- 

 vestigation. Starting with a large quantity of a group of the rare earths 

 in a state of considerable ^Durity, a particular method of fractionation is 

 applied, splitting the earths into a series of fractions differing but slightly 

 from each other. Each of these fractions, phosphorescing i)i vacuo, is 

 arranged in the spectrograph, and a record of its spectrum photographed 

 upon a specially prepared sensitive film. 



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

 bands were recorded — some moderately strong, others exceedingly faint. 

 Selecting a portion giving a definite set of bands, new methods of frac- 

 tionation were applied, constantly photographing and measuring the 

 spectrum of each fraction. Sometimes many weeks of hard experiment 

 failed to produce any .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 

 various groups. Then, taking a group which seemed to offer possibilities 

 of reasonably quick result, one method after another of chemical attack 

 was adopted, with the ultimate result of freeing the group from its accom- 

 panying fellows and increasing its intensity and detail. 



As I have said, my researches are far from complete, but about one of 

 the bodies I may .speak definitely. High up in 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 puri- 

 fication these lines grew stronger. Their great refrangibility cut them off 



' In tliis direction I am glad to acknowleilge my indebtedness to Dr. Schuiiian, of 

 Leipzig, for valuable suggestions and dot;ul 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. 



