802 Are the Chemical Elements [December, 
in the eledtric arc. (The complete spedtrum of the sun, on 
the scale of the working map, will be half a furlong long : 
in mapping the metallic lines and purifying the spedtra 
more than 100,000 observations were made, and about 
2000 photographs taken.) The final discussion of the com- 
plete photographs of the spedtra of the metallic elements 
compared with the spedtrum of the sun led to the results 
which are exciting so much interest at the present time. 
There are certain lines in the spedtra of each element 
which appear long and thick ; and it has been found that 
while such a line, for instance, is exceedingly prominent in 
some one element, other elements appear to possess it, only 
not nearly so prominently. Mr. Lockyer argued from this, 
that on the assumption that the elements are truly ele- 
mentary, the line in the other elements was caused by traces 
of impurity. He has, however, found that there are coin- 
cidences in the lines of metallic spedtra of two perfedtly 
distindt kinds. There are coincidences of lines which are 
not the prominent lines of any one spedtrum, and they give 
no signs of that variability of brightness that might be 
expedted to charadterise lines due to impurities : these lines 
he has called basic lines. In Mr. Lockyer’s own words, 
“ The temperature of the sun and the eledtric arc is high 
enough to dissociate some of the so-called chemical elements, 
and give us a glimpse of the spedtra of their bases, just as 
in the case of the various salts of calcium there is a tem- 
perature which just allows us to get a glimpse of a line 
indicating the metal calcium common to them all.” 
To determine whether these basic lines varied in their 
behaviour from other lines of spedtra taken at random, Mr. 
Lockyer had recourse to the spedtrum of sun-spots. The 
sun is surrounded by an enormous atmosphere which is 
supposed to contain the vapours of such metals as iron and 
magnesium ; but whether this be so or not, Mr. Lockyer 
argued that the atmosphere would certainly be hotter at 
bottom — nearer the photosphere — than higher up, and that 
the spedtrum of the atmosphere close to the photosphere 
would differ from that of any higher region, and therefore 
from the general spedtrum of the sun. In observing the 
spedtrum of a sun-spot, or a prominence, the spedtrum of 
an isolated mass of vapours in the hottest region open to 
inquiry can be determined, and Mr. Lockyer found that this 
spedtrum differed greatly from the general spedtrum of the 
sun. The whole charadter of the spedtrum of iron, for in- 
stance, is changed when we pass from the iron lines seen 
among the Fraunhofer lines to those seen among the spot 
