984 
PROFESSOR J. Iv. LOCKYER ON THE PHOTOGRAPHIC 
lines of iron near F; another the spectra of manganese, nickel, Lenarto meteorite, 
and iron from about G to H ; whilst the third was a comparison of the spectra of 
calcium and barium with the solar spectrum. 
The subject was subsequently referred to in communications to the Royal Society,"^ in 
1874; and with regard to the method of treatment for the elimination of lines due to 
impurities, I remarked : “ The spectrum of the element is first confronted with the 
spectra of substances most likely to be present as imj)urities, and with those of metals, 
which, according to Thalen’s measurements, contain in their spectra coincident lines. 
Lines due to impurities, if any are thus traced, are marked for omission from the 
map and their true sources recorded, while any line that is observed to vary in length 
and thickness in the various photographs is at once suspected to be an impurity line, 
and, if traced to such, is likewise marked for omission.” This work was very 
laborious, and I appealed “ to some other man of science, if not in England, then in 
some other country, to come forward to aid in the work, which it is improbable that 
I, with my small observational means and limited time, can carry to a termination.” 
Thalen’s Eye Observations. 
In 1884, Thalen published a most important paper on the spectrum of iron which 
surpassed in completeness everything before it.t 
He gives a list of 1,200 lines in the arc spectrum of iron which he had observed to 
be coincident with dark lines in the solar spectrum. His observations were made 
between the wave-lengths 3996’7 and 7591’3, that is, from near the Fraunhofer line 
H to A. Between X3996'7 and X5159'6, Thalen determined the wave-lengths of the 
iron lines by comparison with lines in Vogel’s map of the solar spectrum.| From 
XSIGO to X5400 the wave-lengths given in Fievez’s map,§ as well as those due to 
Vogel, were utilised. The positions of lines between X5400 and X6379 were 
determined with reference to Fievez’s lines amd the lines in Angstrom’s spectrum. [j 
From X6379 to the Fraunhofer line A, the positions were determined by micrometer 
measures, and a comparison was made with the iron lines mapped by Angstrom in 
this region. 
A Gramme machine, making 900 revolutions a minute, was used by Thalen to 
produce the electric arc. Rods of iron, 9 millims. in diameter, were first arranged as 
poles, but owing to the long time it was necessary to run the current in order to 
make the observations, the poles got melted. One carbon and one iron pole were 
then tried, and by taking observations with a long arc, it was found possible to get 
* ‘ Roy. Soc. Proc.,’ vol. 23, p. 152 ; ‘ Phil. Trans.,’ vol. 164, p. 805. 
t ‘ Societe Royale des Sciences d’Upsal,’ September 26, 1884. 
I ‘ Publicationen des Astrophys. Observatorium zu Potsdam,’ 1879, No. 3. 
§ ‘ Annales de I’Observatoire Royal de Bruxelles,’ 1883, vol. 4. 
II ‘ Spectre Normal du Soleil, Upsala,’ 1868. 
