Mr, J.H.N. Hennessey on White Lines in Solar Spectrum, 305 



By J. H. N. Hen- 



" On White Lines in the Solar Spectrum." 

 nessey, F.B.A.S. 



Extract from a Letter from Mr. Hennessey to Professor StoTces. 



" Mussoorie, Nov. 12, 1873. 



" My dear Sib, — As I cannot account for what is described and 

 drawn in enclosed, I hasten to place the same before you, intending 

 to look for the white lines in question so soon as I move down to 

 a lower altitude. Amongst others, no doubt Kirchhoff" closely ex- 

 amined the region in question, without notice of the lines ; and this 

 only adds to my perplexity, unless what I see here is due (1) to 

 altitude, or (2) is instrumental. In the latter case I cannot ac- 

 count for the absence of the white lines at Dehra, where I ex- 

 amined the spectrum generally several times ; I must, however, add 

 that without close examination and some experience, the lines 

 might easily be passed over. But if instrumental, to what are they 

 due ? I very much regret that the old spectroscope is not avail- 

 able at present [it had been temporarily sent elsewhere for a special 

 object] to enable me to verify the phenomena " 



[In the drawing sent by Mr. Hennessey, the intervals between 

 the dark lines are coloured green, except in the place of the two 

 white lines. To transfer this distinction to a woodcut, an additional 

 horizontal band has been added below, in which only those parts 

 of the drawing which are left white appear as white, while in the 

 upper part the white of the woodcut represents the white or green, 

 as the case may be, of the original. — Gr. Gr. S.] - T 



Part of Solar Spectrum, drawn to Kirchhoffi's scale, observed at Mus- 

 soorie, N. W. Provinces, India, Lat. N. 30° 28', Long. E. 78° 4' ; 

 Height 6700 feet above sea (about), with the Spectroscope belonging 

 to the Royal Society. 



Note for diagram. — In course of studying the solar spectrum for 

 atmospheric lines, with an excellent 3-prism (new) spectroscope 

 belonging to the Royal Society, I gradually extended mv search, 



Phil. Mag. S. 4. Vol. 48. No. 318. Oct. 1874. ' X 



