xviii.] CALCIUM. 241 



lithium. I reproduce Fig. 75. The question is, can we arrange 

 these spectra along any one line ? and if so, does this line 

 represent a change of temperature merely ? Fig. 89 shows the 

 result of this inquiry. It will be seen how in all essentials it 

 reproduces our hypothetical diagram, Fig. 87. 



The effect of temperature on the spectrum of calcium may be 

 stated as follows : 



(1) At a low temperature we get a spectrum of calcium which 

 contains no lines whatever in the blue ; (2) When we increase 

 that temperature the temperature of a Bunsen burner is some- 

 times sufficient we get a line in the blue at wave-length 4226 -3. 

 (3) When we pass from a Bunsen burner to an electric lamp 

 we get this blue line intensified, and at the same time we get 

 two new lines in the violet, named H and K, at wave-lengths 3933 

 and 3968. (4) Using a still higher temperature in the arc, we 

 thin the blue line, and at the expense of that line, so to speak, 

 we thicken the two in the violet, so that the latter equal the 

 blue line in thickness and intensity. (5) Passing to a large 

 induction coil with a small jar we make the violet lines very 

 much more prominent ; (6) and using a larger induction coil 

 and the largest jar we can get, we practically abolish the blue 

 line and get the violet lines alone. Note that we have simply 

 produced these effects by varying the temperature. 



Figs. 90 and 91 enable us to see what happens in the case of 

 magnesium ; how disorder is at once abolished, and how exactly 

 the same order is brought about by the same progression as 

 in the case of calcium, from flame through arc, spark, sun 

 (general) to prominences, the last term in both series. 



Next comes the case of lithium (Figs. 92 and 93). 



As before, we find order brought about and the hypothetical 

 diagram reproduced by the same series of increasing temper- 

 atures, but here the last term in the series is wanting, for so far 

 no line of lithium has been seen bright in the prominences. 



That in the case of the blue line we are really dealing with 



K 



