74 Intelligence and Miscellaneous Articles* 



centimetres, for example, I have been able to ascertain that the mag- 

 nitude of the absorption due to the first 10 centimetres was greater 

 than that of the ten following, and so on. I do not dwell upon this 

 point, for I was not able to work with homogeneous rays. 



I have not spoken in this note of the experiments I have made 

 with bisulphide of carbon. Its action, whether liquid or gaseous, 

 was so small that I could not deduce anything definite from its study 

 as regards the principal fact to which I call the attention of the 

 Academy. — Comptes Rendus, May 27, 1867. 



ON THE SPECTRUM OF MARS, WITH SOME REMARKS ON THE 

 COLOUR OF THAT PLANET. BY WILLIAM HUGGINS, F.R S. 



On several occasions during the late opposition of Mars, I made 

 observations of the spectrum of the solar light reflected from that 

 planet. 



The spectroscope which I employed was the same as that of which 

 a description has appeared in my former papers*. Two instruments 

 were used, one of which is furnished with a single prism of dense 

 glass, which has a refracting angle of 60°. The other instrument 

 has two similar prisms. 



In a paper " On the Spectra of some of the Fixed Stars," by my- 

 self and Dr. W. A. Miller, we state that on one occasion several 

 strong lines of absorption were seen in the more refrangible parts of 

 the spectrum of Mars. 



During the recent more favourable opportunities of viewing Mars, 

 I again saw groups of lines in the blue and indigo parts of the spec- 

 trum. However, the faintness of this portion of the spectrum, when 

 the slit was made sufficiently narrow for the distinct observation of 

 the lines of Fraunhofer, did not permit me to measure with accuracy 

 the position of the lines which I saw. For this reason I was unable 

 to determine whether these lines are those which occur in this part 

 of the solar spectrum, or whether any of them are new lines due to 

 an absorption which the light suffers by reflexion from the planet. 



I have confirmed our former observation that several strong lines 

 exist in the red portion of the spectrum. Fraunhofer's C was di- 

 stinctly seen, and its identity determined by satisfactory measures 

 with the micrometer of the spectrum-apparatus. From this line 

 the spectrum, as far as it can be traced towards the less refrangible 

 end, is crossed by dark lines. One strong line was satisfactorily 

 determined by the micrometer to be situated near C, at about one- 

 fourth of the distance from C to B. As a similar line is not found 

 in this position in the solar spectrum, the line in the spectrum of 

 Mars may be accepted as an indication of absorption by the planet, 



* « On the Spectra of some of the Fixed Stars," Phil. Trans. 1864, p. 415. 

 During my prismatic researches I have tried, and used occasionally, several 

 other arrangements for applying the prism to the telescope. Some of these 

 instruments are fitted with compound prisms, which give direct vision. I 

 have not found any apparatus equal in delicacy and in accuracy to that which 

 is referred to in the text. 



