Intelligence and Miscellaneous Articles. 569 



since it is an absurd compound ; and the half English word " fel- 

 stone " is no less objectionable. Neither could ever find place in 

 any European work on lithology. 



Felsite is an old word in the science, used by mineralogists of all 

 lands. 



ON THE DISPLACEMENT OF THE LINES IN THE SPECTRA OF THE 

 STARS, PRODUCED BY THEIR MOTION IN SPACE. BY FATHER 

 SECCHI. 



Rome, March 25, 1876. 



It is now generally admitted, in accordance with the ideas put 

 forth by Doppler in 1842, that the displacement of a luminous point 

 which is moving from or approaching towards the observer produces 

 an alteration in the length of the light- wave. Prom this principle, 

 combined with those of spectral analysis, it follows that the lines of 

 a substance existing in a star in motion will be displaced in relation 

 to those obtained with the same substance on the earth. The amount 

 of the displacement will depend on the velocity of the star in the 

 direction of the line of sight of the observer. Objections to this 

 theory have not been wanting ; but it appears to have been generally 

 received*, and confirmed by the observation of curvatures in the 

 lines of the solar protuberances. 



To ascertain the rigorous accuracy of this theory I made some 

 experiments in 1863 ; but the results at that time were negative. 

 I attributed the want of success to the inadequacy of my instru- 

 ments. A little while after, Mr. Huggins resumed the question, 

 and found some sensible displacements, of which he gave an account 

 to the Royal Society of London ; but, fearing nevertheless an illu- 

 sion produced by the manner of illuminating the slit, he made some 

 changes in his procedure and examined several stars afresh. In 1872 

 he gave a list of motions judged to be definitive f. 



In this interval I was often occupied with the subject, especially 

 in 1868 J, employing sometimes processes of comparison, sometimes 

 absolute methods ; but my results did not always agree with those 

 of the celebrated English spectroscopist. Nevertheless, out of regard 

 for his great authority, and taking into consideration the very per- 

 fect means he had at his disposal, I was led to prefer his results, 

 notwithstanding their opposition to my own. Lately M. Vogel, at 

 Bothkamp, and the Greenwich Astronomers having published some 

 researches on the subject, I found in their results some considerable 

 divergences from those of Mr. Huggins ; and I determined to resume 

 the experiments and make a new examination of the question. 



In the following Table I sum up the results of a determination, 

 marking with the sign + the cases of increasing, and with the sign — 

 those of diminishing distance : — 



* M. Van der Willingen, however, has contested it. 



t See ' Nature,' vol. vi. p. 135, July 1872. 



X See Comptes Rendus de V Acad, des Sciences, March 2, 1868. 



Phil. Mag. S. 5. No. 7. Suppl. Vol. 1. 2 Q 



