f FLAMES OF COMPOUNDS OF CARBON AND HYDROGEN. 423 
i proved so successful, that I venture to describe it, in the hope that it may prove 
useful in similar researches. A hole, @ (see fig. 4), 0-1 inch in diameter, was 
drilled in the side of the tube in which the eye piece slides, at a point between the 
field lens of the eye piece and the wires w; a small lamp, L, furnished with a 
condensing lens ¢, and a conical tube with a small aperture ¢, through which 
alone light was allowed to pass, was attached to the telescope, so that the light, 
indicated by 77, emerging from the conical tube, and entering the hole in the 
eye piece tube, crossed the axis of the telescope at an angle of about 70°, so as to 
illuminate the intersection of the wires at w, on the side neat the eye, while all the 
rest of the field remained perfectly dark. By slightly varying the position of the 
lamp, the illumination of the wires could be adjusted with the utmost nicety to. 
suit the brightness of that portion of the spectrum which was under examina- 
t tion. 
Notwithstanding the most careful adjustment of the illumination of the wires, 
| I still found the observation of the fainter lines of the carbohydrogen spectrum 
extremely difficult. The brightness of the lines in the spectrum of the Bunsen 
lamp is, however, considerably augmented by urging the flame by the blowpipe ; 
and I found it useful to employ three jets placed one behind another, so that the 
combined illumination of three blowpipe cones might fall upon the prism. This 
___ apparatus, which is useful in exhibiting the fainter lines of the carbohydrogen 
___ spectrum, is easily constructed by forming three blowpipe jets of glass tube, about 
0-2 inch in diameter, in the ordinary manner, and placing them, side by side, in 
a perforated cork. The cork is then inserted in a short piece of wide tube, having 
at its other end a second cork, connected with a flexible tube conveying a current 
of air from a table blowpipe. 
} _ Ihave also carefully compared, by simultaneous observations, the spectrum 
of the Bunsen lamp fiame urged by a jet of oxygen gas, with the spectrum ob- 
| __ tained by means of the triple air blowpipe. The lines in the two spectra were 
almost equally bright, and differed neither in number nor in position. 
'____In the observations, Series I., Tables II. and III., I used an eye piece giving a 
_ Imagnifying power of 11, which was afterwards superseded by another magnify- 
ing 21 times, with which Series II. was made. 
Comparison of the Carbohydrogen and Solar Spectra. 
The second series of observations having been made with a higher magnify- 
ing power, and in some other respects also in more favourable circumstances 
than the first, is to be regarded as more trustworthy ; yet the results of both agree 
80 closely, that any additional accuracy which might have been obtained by as- 
certaining, separately, the probable errors of the two series, and their most pro- 
| _ bable result, when combined, could scarcely have repaid the labour of the neces- 
_ sary computation. I have, therefore, deemed it sufficient to give all the observa- 
VOL. XXI. PART III. ; 5Y 
