THE ULTRA-VIOLET SPECTRA OF THE ELEMENTS. 
217 
Strontium. 
Strontium, and its compounds, produce a line at wave-length 3705 coincident, or 
nearly so, with one of the lines ascribed to calcium by Cornu. We have so often 
observed this line much reinforced by strontium without any increase of the other 
calcium lines which are always present in the arc from calcium in the carbon electrodes, 
that Ve think we are justified in putting down a strontium line at this place. Two 
other lines of this metal are close to, but not coincident with lines of barium. 
Strontium lines. 
Approximate 
wave-length. 
u 
Remarks. 
Approximate 
wave-leDgth. 
Remarks. 
3705-0 
Coincident or nearly so with a 
3458-0 
Diffuse. 
calcium line. 
3379-5 
3653-0 
3364-8 
3547-0 
3305-2 
3527-0 
2931-1 
3498-0 
3464-0 
Calcium. 
Cornu has mapped two calcium lines, one on either side of the solar line M, and 
four other lines, of which one is coincident with the solar line R, one slightly less 
refrangible, and the other two more refrangible. One of these lines, at wave-length 
3168*5, we have never certainly seen, but the others are well developed when calcium 
compounds are put into the arc. Besides these we have always seen when calcium, or 
one of its compounds, is present in moderate quantity a series of triplets analogous to 
those of magnesium. Each triplet consists of two strong lines with a rather weaker 
line on their more refrangible side. This series appears to be harmonically related to 
the well-known blue triplet at wave-length 4454-24. The first repetition of this 
triplet occurs close to H, one line of the triplet falling below H, while the other two 
lines fall between H and K. The next triplet falls between N and M, and the next 
between O and N, and so on at decreasing intervals, the most refrangible repetitions 
becoming very faint and diffuse, so that in the last, a little below S, we have only 
been able to distinguish the strongest two lines of the triplet. The triplets are 
alternately diffuse and sharp, those near H, between 0 and N, and so on alternately, 
being the sharper. The diffuse triplets are stronger than the others and more easily 
reversed. Beyond this series we have noticed only one calcium line, and that is high 
up on the scale, at wave-length about 2398. 
2 F 
mdccclxxxiii. 
