xiv.] CALCIUM. 195 



calcium; for H and K, the two most marked lines in the solar 

 spectrum, are really coincident with calcium lines. 



But with which ? With precisely those not seen at all in 

 some cases. And how then about the very strong line of calcium 

 seen in the electric arc, a line excelling all others in brilliancy ? 

 In the solar spectrum it is a poor, feeble line. 



Let us next pass to the prominences. I have already stated 

 that Young's relative numbers for H, K, and the blue line, are 

 75, 50, and 8 ! Even this is not the only differentiation possible. 

 Young, in his work at Sherman, saw the H and K lines brightened 

 over every important spot, and he never saw the blue line 

 brightened at all. 



In the case of calcium, at all events, then, both on the 

 terrestrial and the solar evidence, whatever the explanation 

 may be, there is the undoubted fact that fundamental changes 

 of intensity in the lines are to be noticed, and if KirchhofFs 

 statement about the matching of the intensities of lines in 

 solar and terrestrial spectra is true for one condition, it is of 

 necessity false for all the others. 



To sum up the facts regarding calcium, we have first of all 

 the H and K lines differentiated from the others by their greater 

 frequency in prominences, their brightening in spots, and their 

 enormous thickness in the general spectrum of the sun. We 

 have the blue line differentiated from H and K by its thinness 

 in the solar spectrum while they are thick, and by its thickness 

 in the arc while they are thin. We have it again differentiated 

 from them by its absence from solar storms in which they are 

 almost universally seen. 



Last stage of all, we have the red lines seen of surpassing 

 brilliancy in the Bunsen flame, while they 'never appear in 

 solar phenomena. 



We next turn to magnesium. The accompanying woodcut 

 gives a generalized view of the phenomena recorded in our 

 laboratories and observatories. 



o 2 



