106 INORGANIC EVOLUTION. [CHAP. 



Only one exception to this general statement was noted at the 

 beginning of the inquiry ; it refers to calcium. " The lines H and K, 

 .among others, shift only about half as much as g (the blue line at 

 A 4226-91), and the group at A 5600. That.? should differ in this 

 respect from H and K is not very surprising, since it is known to differ 

 greatly from them in many other respects." 



On this exceptional behaviour of these lines of calcium, I quote the 

 following, from a note by Professor Hale.* 



" The difference in behaviour of H and K and the blue line of 

 calcium discovered by Messrs. Jewell, Humphreys, and Mohler, seems 

 to support Lockyer's views as to the dissociation of calcium in the arc 

 and sun. The remarkable variations of the calcium spectrum with 

 temperature have long been known principally through the investiga- 

 tions of Lockyer. The writer has shown that the H and K lines are 

 produced at the temperature of burning magnesium and in the oxy- 

 coal-gas flame. They could not be photographed in the spectrum of 

 the Bunsen burner, though an exposure of sixty-four hours was given. 

 Since these experiments were made, I have been informed by Professor 

 Eder that his own efforts to photograph the lines in the Bunsen burner 

 were no more successful, though an optical train of quartz and fluor- 

 spar was employed. It would thus appear that the temperature of the 

 dissociation of calcium is between that of the Bunsen burner and that 

 of the oxy-coal-gas flame. The high molecular weight of calcium has 

 hitherto conflicted with our belief in the presence of this metal in 

 prominences. If, however, it be granted that dissociation can be 

 brought about by temperatures even lower than that of the arc, the 

 difficulty is very greatly lessened." 



In an article which I wrote in Nature on this work,f I pointed out 

 that " it would be very interesting to see if the strontium line at 

 A 4607*52 behaves like the calcium g in relation to the lines at A 4077-88 

 and A 4215-66, representing H and K." 



This prediction was subsequently confirmed by Mr. Humphreys, J 

 who gave a table of the shifts measured on the strontium lines mentioned 

 above. When working with pressures varying from 6 to 12 atmo- 

 spheres, the shift of the line at A 4077*88 was always approximately 

 half that at A 4607-52. 



There can be little doubt after this successful prediction that other 

 enhanced lines will follow suit as this new attack is carried further. 



* Astrophysical Journal, loc. cit. 

 t Nature, vol. liii, p. 416, March, 1896. 



J " The Effect of Pressure on the Wave-lengths of lines in the Spectra of certain 

 Elements," Asirophysical Journal, vol. iv, p. 249. 



