IX CONNEXION WITH THE SPECTRUM OF THE SUN. 
261 
at present are preliminary only, were made because it seemed clear that the same law 
that was observed with the chlorides should hold good. 
A cursory examination of the spectra of some amalgams of tin and magnesium has 
shown that this is the case. 
For instance, it is possible to begin with an alloy which shall only give us the longest 
line or lines in the spectrum of the smallest constituent, and by increasing the quantity 
of this constituent the other lines can be introduced in the order of their length. This 
reaction is so delicate that I learnt from it a thing I had not before observed, that the 
least refrangible line of b, the triple line of magnesium, is really a little longer than its 
more refrangible companion ; for the spectrum of magnesium was reduced to this one 
line in an alloy in which special precautions had been taken to introduce the minimum 
of magnesium. 
It follows from this statement that not only is the spectrum-analysis almost infinitely 
more delicate than it has hitherto been supposed to be in the case of the elements in 
which the difference between the longest and shortest lines is least*', but that in time 
it may become quantitative ; for if the admixture of certain other bodies extinguishes 
the shorter lines of metallic spectra, it would seem that a series of carefully executed 
maps of the spectra of alloys, the proportions of the constituents of which are known, 
will place in our hands the means of determining (roughly it is true) by mere inspection 
the quantity of the sought metal present in an alloy, the composition of which qua that 
metal is unknown. At the same time it is clear that further progress must be made 
before such a method can be practically employed in the arts. 
Although the working hypothesis which has suggested the various lines of research 
which have been followed is, I think, sufficiently clear, I refrain from dwelling upon 
it until other researches now in progress enable me more fully to judge of its value, and 
to state at greater length the various conclusions which may be drawn from it. 
Application of these Observations to the Solar Spectrum. 
These observations have an important bearing upon the solar spectrum, for the reason 
that, as is well known, all the lines known to exist in the spectrum of an element sup- 
posed to be present in the sun’s atmosphere are not in all cases reversed. 
Before I proceed to give the facts in detail it will be well to go over the prior work 
of Kirchhoff and Angstrom, to see precisely the evidence on which our present know- 
ledge of the elements in the solar atmosphere, as determined by Kirchhoff’s method of 
solar observation (that is, the non-localization or integration of the various solar 
regions, such as spots, facuke and chromosphere), rests. 
Kirchhoff, in his paper referring to Fraunhofer’s prior determination of the double 
line D being coincident with a double line observed in the spectrum of sodium vapour, 
locates sodium vapour in the solar atmosphere, as Professor Stokes had done before him, 
* The great lengths of the lines of sodium, lithium, &c. at once account for the delicacy of their spectrum 
reactions. 
2 N 
MDCCCLXXIII. 
