Intelligence and Miscellaneous Articles. 239 



earths in the ultra-violet rays*, I hasten, with a view to my own 

 interest, to bring to the knowledge of the Academy that the earth 

 designated X was discovered by me more than a year ago : the dis- 

 covery was publicly announced, in the course of the proceedings of 

 the Philadelphia Academy of Natural Sciences, in May 1877 1; a 

 communication to the same effect was also sent to the said Academy 

 in -November of the same year. 



My conclusions were based entirely on chemical principles ; for 

 it was proved that the earth which I had discovered was distin- 

 guished by its properties from all those known to belong to the 

 yttria and cerium groups, although it came very near those earths, 

 the chemical properties of which shade almost insensibly into one 

 another. A short time after announcing the discovery, I sent a 

 specimen to M. Delaf ontaine, of Chicago, who thought that it would 

 prove to be either Mosander's terbia or some new earth. It was, 

 however, impossible for me to make its properties agree with those 

 at that time attributed to terbia. 



I was desirous as far as possible to rid this new earth of the pre- 

 sence of earths already known, in order to study its properties and 

 constituent parts. For better success I required a little of the 

 terbia which M. Marignac had recently extracted from gadolinite. 

 I wrote therefore, in March, to that able chemist. He possessed 

 too small a quantity of that earth to let me have any ; but he ex- 

 amined my new earth and the nitrate, which I sent to him ; and in 

 communicating to me the result of his examination he says (inter 

 alia), " Not only am I convinced of the identity of your earth and 

 my terbia, but I may add that you have obtained it in greater purity 

 than I." After M. Soret had examined my earth by means of the 

 spectroscope, he said to me, "I can have no doubt about the iden- 

 tity of that chemist's^ [M. Delaf ontaine's] and my terbia and your 

 earth." 



The spectroscopic observation of M. Soret placed beyond doubt 

 that the earths of samarskite contain a new metal, as I announced 

 in May 1877, my first specimen then obtained giving the absorp- 

 tion-spectrum marked No. 2 in his communication. I no longer 

 hesitate to give to this metal the name of mosandrum, in honour of 

 the distinguished chemist whose researches and remarkable disco- 

 veries in this class of earths form a brilliant epoch in the history of 

 metallic chemistry. 



In giving the following succinct history of this discovery, I 



* This has no relation to the Ural samarskite, in which I, concurrently 

 with other chemists, have found oxide of cerium. 



t Comptes Rendus, April 29, 1878. 



" Professor Lawrence Smith made some observations on the anomalous 

 properties of the earthy oxides of samarskite, and stated the reasons which 

 led him to believe that those oxides do not contain cerium, and that most 

 of what is regarded as cerium is a new element.' 1 — Annals of the Phila- 

 detyhia Academy of Natural Sciences, May 8, 1877. 



% In the course of more recent researches M. Delafontaine believed he 

 had discovered another new earth ; but M. Soret's experiments and M. 

 Marignac's conclusions make it evident that this earth is identical with 

 that discovered by me. 



