10 Mr. H. Eamage. Relations of Spectra, Densities, [Nov. 7, 



The four lines occur in the arc spectra of their respective elements : 

 the zinc line is in Kayser's and Eunge's tables, marked 8r ; the mag- 

 nesium line 4574 is marked 4, the remaining two lOr. These charac- 

 ters indicate that the magnesium line A. 2852 corresponds to the lines 

 of zinc and cadmium. The magnesium line A 2852 has not been 

 examined under the Zeeman effect, but the zinc line breaks up into a 

 "very sharp triplet " and the cadmium line into a "triplet" (Eeese). 

 The magnesium line is given when a very small quantity of the element 

 is heated in the oxyhydrogen flame, or by a very short exposure ; it 

 furnishes, in fact, a delicate test for the element. All this evidence 

 indicates that the line A, 2852 corresponds to the zinc and cadmium 

 lines. 



Eydberg says (p. 106) of the magnesium line X 2852 : " It is prob- 

 able. . . . (it) corresponds to the strongest lines in the spectra of 

 the elements : " — Calcium 4226, strontium 4607, and barium 5534. 

 The evidence furnished by the oxyhydrogen flame spectra is against 

 this conclusion, for it shows no similarity between the spectrum of 

 magnesium and those of the calcium group. The bands in the flame 

 spectra of the calcium group are degraded on the less refrangible side, 

 and they are quite different in character from those of the zinc group. 



Eydberg says (p. 114) that the lines of zinc 3075*6 and cadmium 

 3260-12 " correspond perfectly." He does not refer to a correspond- 

 ing line in the spectrum of mercury. There is one, doubtless, and its 

 discovery will be of considerable interest. 



Ames* selected the following lines from the arc spectra. Magnesium 

 2852-2, zinc 2138'3, and cadmium 2288-1. These lines of zinc and 

 cadmium have not been observed in the oxyhydrogen spectra. Even 

 if present they must, on account of their high refrangibility, be very 

 weak. The zinc line X 3076, lies, in the flame spectrum, among the 

 lines in the strongest water vapour group, and it was photographed for 

 the first time, in a special search for it, in May, 1900. 



The Aluminium Group. — All the lines found in the flame spectra of 

 the metals of this group are used in the investigation. The selection 

 of the corresponding lines presents no difficulty, as the corresponding 

 lines are clearly indicated by the relative intensity of the lines, and 

 by the fact that the less refrangible member of one series of doublets 

 is itself double. Five lines have been observed in the flame spectrum 

 of gallium, but this spectrum has not been fully examined. The 

 wave-lengths of the other five lines were determined on two photo- 

 graphs of the spark spectrum of gallium which Professor Liveing very 

 kindly lent me. 



Exner and Haschek have measured some lines in the spark spectrum 

 of gallium. f 



* Loc. ext. 



f ' Akad. Wiss. Wien, Sitzb.,' 108, p. 1120, 1899. 



