212 Phosphorescent Spectra in High Vacua. [May 19, 



spectrum, and it is only occasionally, and as it were by accident, that 

 I have so entirely separated it from the anomalous earth as to see the 

 bands in their full purity. Another earthy body gives a spectrum 

 similar to that just described, but wanting the red, and having a 

 double orange and double citron band. A third gives a similar 

 spectrum, but with a yellow line interposed between the double 

 orange and the double citron, and having two narrow green lines. 



At present I do not wish to say more than that I have strong 

 indications that one, or perhaps several new elements are here giving 

 signs of their existence. The quantities I have to work upon are 

 very small, and when each step in the chemical operation has to be 

 checked by an appeal to the vacuum tube and to the induction coil 

 the progress is tediously slow. In the thallium research it only 

 occupied a few minutes to take a portion of a precipitate on a 

 platinum loop, introduce it into a spirit-flame, and look in the spectro- 

 scope for the green line. In that way the chemical behaviour of the 

 new element with reagents could be ascertained with rapidity, and a 

 scheme could be promptly devised for its separation from accompany- 

 ing impurities. Here, however, the case is different : to perform a 

 spectrum test, the body under examination must be put in a tube and 

 exhausted to a very high point before the spectroscope can be brought 

 to bear on it. Instead of two minutes, half a day is occupied in 

 each operation, and the tentative gropings in the dark, unavoidable in 

 such researches, must be extended over a long period of time. 



The chemist must also be on his guard against certain pitfalls 

 which catch the unwary. I allude to the profound modification which 

 the presence of fluorine, phosphorus, boron, &c, causes in the 

 chemical reactions of many elements, and to the interfering action of 

 a large quantity of one body on the chemical properties of another 

 which may be present in small quantities. 



The fact of giving a discontinuous phosphorescent spectrum is in 

 itself quite insufficient to establish the existence of a new body. At 

 present it can only be employed as a useful test to supplement 

 chemical research. When, however, I find that the same spectrum- 

 forming earthy body can always be obtained by submitting the 

 mineral to a certain chemical treatment; when the chemical actions 

 which have separated this anomalous earth are such that only a 

 limited number of elements can possibly be present ; when I find it 

 impossible to produce a substance giving a similar discontinuous 

 spectrum by mixing together any or all of the bodies which alone 

 could survive the aforesaid chemical treatment ; when all. these facts 

 are taken into consideration, and when due weight is given to the 

 very characteristic spectrum reaction, I cannot help concluding that 

 the most probable explanation is that these anomalies are caused by 

 the presence of an unknown body whose chemical reactions are not 



