FLAMES OF COMPOUNDS OF CARBON AND HYDROGEN. 423 



proved so successful, that I venture to describe it, in the hope that it may prove 

 useful in similar researches. A hole, a (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 iv ; a small lamp, L, furnished with a 

 condensing lens c, and a conical tube with a small aperture e, through which 

 alone light was allowed to pass, was attached to the telescope, so that the light, 

 indicated by r r, 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 next 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- 

 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. 



I have also carefully compared, by simultaneous observations, the spectrum 

 of the Bunsen lamp flame 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 

 magnifying power of 11, which was afterwards superseded by another magnify- 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 

 so 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. 5 Y 



