Showing their identity with two lines in the Solar Spectrum. 3 
Plate II1.—A second plate with the same two spectra, a band of the solar 
spectrum running through the middle of the spectrum, and a 
second one touching the edges of the lines. 
Plate IV.—(1) An are spectrum of pure iron, the metal being prepared from 
potassium ferrocyanide, by fusion with potassium carbonate. 
(2) The same. 
(3) The same, with a large proportion of the residue obtained on 
ignition of gallium ferrocyanide. 
(4) Similar to (3), but with a smaller proportion of gallium. 
(5) Solar spectrum photographed on the succeeding day, the sun 
at the time being too low to show possible coincidences. 
In (3) and (4), the gallium lines are beautifully reversed; but in (4), the lines 
are broad and the reversals much less marked. The reversed lines of gallium are 
clearly seen to correspond with reversals in the solar spectrum; but the reversals 
may probably be those of iron lines very closely adjacent to those of gallium. 
Plate V.im(1) Are spectrum of pure iron from ferrocyanide, with the addition 
of a gallium compound, on the middle portion only. The 
solar spectrum is taken with the middle portion cut out. 
(2) Are spectrum of a small quantity of a gallium compound and a 
small quantity of the iron also, with the solar spectrum 
as in (1). 
In the oxyhydrogen flame, arc and spark spectra of substances both poor and 
rich in gallium, the line 4172 is always stronger than 4033. 
By measurements of the iron lines and the gallium lines in are spectra of 
materials containing different proportions of the two metals, the wave-lengths of 
the two gallium lines were determined by interpolation from the iron lines. The 
wave-lengths of the latter used were those determined by Rowland in the solar 
spectrum. By this method, the wave-lengths of the reversed gallium lines are 
found to be 4172:214 and 4033°125. These numbers are higher than those 
obtained by Lecocq de Boisbaudran in the spark, and higher also than our 
measurements of the lines in the oxyhydrogen spectra photographed with very 
small dispersion, namely, 4171°6 and 4032-7; but they have been verified to the 
second decimal place by different measurements. 
In Rowland’s Table of Solar Spectrum Wave-lengths, published in the“ Astro- 
Physical Journal,” vol, i,, pp. 139 and 225, there are two lines corresponding to 
these; but, to judge of the probability of these lines belonging to the element 
gallium, it is necessary to consider their relative intensities. Rowland measures 
