x.] THE "SERIES" EVIDENCE. 97 



case of magnesium, calcium and strontium, and also aluminium, zinc, 

 and tellurium; we have a first and second subordinate series, but 

 no principal series. I have studied- the lines of calcium and mag- 

 nesium, in the same way that the lines of oxygen were studied, to see 

 how many of the lines are picked up by the series, and I proceed to 

 furnish some details. In the upper part of the diagram (Fig. 34) I 

 give the lines seen in the arc spectrum of calcium, and in the two next 

 horizons we have the lines picked up in the first and second subordinate 

 series. The next horizon gives the residual lines lines, that is, which 

 are not distributable among these series. We see that there is a large 

 number outstanding just as in the case of oxygen, and it is very im- 

 portant indeed to note that the two lines H and K, which are more 

 conspicuous in the spectrum of the sun than all the other lines of the 

 spectrum, have not been caught by any of these researchers into the 

 series of calcium. Therefore, with a reduced number of series, we seem 

 to be getting still further from the simplicity we began with in the 

 case of some of the permanent gases like hydrogen and helium. The 

 game thing holds with regard to magnesium, the spectrum of which at 

 the temperature of the arc has not so many lines in it as the spectrum 

 of calcium. A certain number of these lines has been picked up to 

 form the series, but we get numerous lines which have been left over 

 after all attempts to sort them into series have been made. 



I have now to refer to another consideration. We have dealt so far 

 in the case of calcium and magnesium with arc temperatures, but I 

 showed on pages 35 and 36 that in the case of these metals at spark 

 temperatures, the spectra are greatly changed, enhanced lines making 

 their appearance ; and I stated on page 57 that the all-important lines 

 in the hottest stars are lines seen at the temperature of the spark. I 

 have added these lines to the diagram, and we see that there is not the 

 slightest trace of those lines having been picked up in the series. So 

 that the further we go, the more we seem to get away from that beauti- 

 ful simplicity with which we began. 



I refer next to another group of substances, namely, tin, lead, 

 arsenic, antimony, bismuth arid gold, and I might mention more. No 

 series whatever have as yet rewarded the many attempts of those who 

 have tried to get those metals and non-metals on all-fours with those 

 previously investigated. As already stated, it remained for Kayser 

 and Eunge to point out that it looked very much as if this complete 

 absence of series was connected with the melting points of the substances 

 with which they had been dealing. So long as the melting point was 

 low, as in the case of sodium and lithium, the normal three series 

 would show at low temperatures ; and, further, there were no lines 

 over. But, when we deal with substances with high melting points, 



H 



