FLAMES OF COMPOUNDS OF CARBON AND HYDROGEN. 419 
Comparison of the Carbohydrogen and Solar Spectra. 
Having ascertained, that probably all substances of the forms C, H, and C, H, O, 
produce, when burning, spectra which are absolutely identical, I was desirous to 
compare their spectra with that of sun light. 
For this purpose I at first attempted to view the solar spectrum and that of 
the Bunsen lamp simultaneously, but the great comparative faintness of the lat- 
ter rendered that mode of comparison exceedingly difficult. I therefore deter- 
_ mined to measure separately the minimum deviations for the principal lines of 
the solar and gas spectra; the intervals between the adjacent smaller lines of the 
latter spectrum being ascertained by means of a micrometer. 
The instruments I employed were an excellent theodolite by Apim, and a very 
fine flint-glass prism by Secreran of Paris, whose faces have an area of four 
square inches, and which shows, with great distinctness, the finest lines in Fraun- 
HOFER’S map of the solar spectrum. Jam indebted for the use of these instru- 
ments to the kindness of Mr Joun Apir and Professor ForseEs. 
The prism being placed in its position of minimum deviation, the indices of 
refraction given in the sequel were calculated by the formula 
_ sint(1+D), 
essing ly 
where I is the angle of the prism, and D the deviation of the transmitted light. 
I have denoted the five brightest lines of the carbohydrogen spectrum by the 
letters, a, G, y, 6, 7; and the fainter lines by which they are accompanied by £,, (,, 
%,, &c. Inthe tables, Dy, Dy, ps, p,, &c., denote respectively the minimum devia- 
tion of the rays, and the index of refraction for the lines A and y of the solar 
and flame spectra. 
A comparative diagram of the spectra of sunlight and the hydrocarbon flames 
is given in Plate VIII., fig. 1, where a is the double yellow line R of FraAuNHOFER. 
 Thave thought it advisable to introduce this line in the diagram, as it is almost 
constantly visible in ordinary artificial light, although, for reasons already fully 
stated, I conceive it is not peculiar to the spectra of carbohydrogen compounds. 
_ This conclusion is strongly corroborated by the remarkable phenomena pointed 
_ out at p. 414, namely, that the salts of sodium tinge the exterior envelope of 
_ the Bunsen lamp flame with so brilliant a yellow light, as completely to over- 
_ power the comparatively feeble blue light of the inner cone, and to render it al- 
_ together invisible; while yet the light of that portion of the flame remains abso- 
_ lutely unchanged. This remarkable property of flame is easily demonstrated by 
holding a slip of platinum, with some salt placed on it, in the flame, while the 
spectrum is observed through a telescope. The instant the salt reaches the flame, 
| the yellow line R or a, which before may have been extremely faint, or altogether 
VOL. XXI. PART II. s 5x 
