490 
ME. J. NORMAN LOCKTEE ON SPECTEUM-ANALYSIS 
instances of the results to be obtained by the confronting of the spectrum of each solar 
metal with every other, a task which it will be necessary to accomplish before the Table 
and Maps referred to can be presented to the Eoyal Society. 
IY. PEELIMINAEY INQUIRY INTO THE EXISTENCE OP ELEMENTS IN THE SUN NOT 
PREVIOUSLY TRACED. 
In a paper communicated to the Eoyal Society on December 12, 1872 (Phil. Trans. 
1873, p. 253), I have shown that the test formerly relied on to decide the presence or 
absence of a metal in the sun (namely, the presence or absence of the brightest and 
strongest lines of the metal in question in the average solar spectrum) was not a final 
one, and that the true test was the presence or absence of the longest lines of the metal, 
this longest line being that which remains longest in the spectrum when the pressure 
of the vapour is reduced. 
Of the test in question I have said, in the paper already mentioned, “ It is one, 
doubtless, which will shortly enable us to determine the presence of new materials in 
the solar atmosphere, and it is seen at once that to the last published table of solar 
elements (that of Thaler) must be added zinc, aluminium, and possibly strontium as a 
result of the new method.” 
In order to pursue the inquiry under the best conditions, complete maps of the long 
and short lines of all the elements are necessary. It was, however, not absolutely neces- 
sary for the purposes of a preliminary inquiry to wait for such a complete set of maps, 
for the lists of lines given by the various observers may be made to serve as a means of 
differentiating between the longest and shortest lines, because I have also shown that 
the lines given at a low temperature, by a feeble percentage composition, or by a 
chemical combination of the vapour to be observed are precisely those lines which 
appear longest when the complete spectrum of the pure dense vapour is studied. 
Now with regard to the various lists and maps published by various observers, it is 
known (1) that very different temperatures were employed to produce the spectra, some 
investigators using the electric arc with great battery-power, others the induction- 
spark with and without the jar ; (2) that some observers employed in certain cases the 
chlorides of the metals the spectra of which they were investigating, others used speci- 
mens of the metals themselves. 
It is obvious, then, that these differences of method could not fail to produce differences 
of result ; and accordingly, in referring to various maps and tables of spectra, we find that 
some include large numbers of lines omitted by others. A reference to these tables, in 
connexion with the methods employed, shows at once that the large lists are those of 
observers using great battery-power or metallic electrodes, the small ones those of 
observers using small battery-power or the chlorides. If the lists of the latter class of 
observers be taken, we shall have only the longest lines, while those omitted by them 
and given by the former class will be the shortest lines. 
In cases, therefore, in which I had not mapped the spectrum by the new method of 
