THE 



PEOCEEDINGS 



OF 



EOT AL SOCIETY. 



June 16, 1870. 



XIV. " On the Atmospheric Lines of the Solar Spectrum, in a Letter 

 to the President." By Lieut. J. H. Hennessey. Communicated 

 by the President. Received May 21, 1870. 



Mussoorie, April 25, 1870. 

 My dear Sir, — I have the pleasure to enclose a map of the solar 

 spectrum, including the region from the extreme red to the lines D, and 

 a report on my endeavours to view the zodiacal light. A complete set of 

 actinometric observations (simultaneous) between Dehra and Mussoorie 

 has also been made. The latter observations are in course of reduction, 

 and will, I trust, be submitted to you ere long. 



2. Instruments. — The set of instruments which the President and 

 Council of the Royal Society were good enough to send out to India under 

 Lieut. Herschel's care, for my use, was duly handed to me at Bangalore 

 (Madras Presidency) when I was on duty there in the winter of 1867-68. 

 This set comprises a spectroscope with three flint-glass prisms, a hand- 

 spectroscope, a tube with a double-image prism, and two of Hodgkinson's 

 actinometers, as detailed in Professor Stokes's letter (list) addressed to the 

 Under Secretary of State for India, dated 31 October, 1867. 



3. Narrative. — On the completion of my duties at Bangalore I was 

 enabled to bring the instruments up to Mussoorie, where the spectroscope 

 was set up in May 1868. Meanwhile, however, the hot season in the 

 plains had set in. The dust, as usual at this time of the year, filled the 

 atmosphere, so that all hopes of obtaining spectroscopic observations of 

 the sun about the time of sunset were in vain ; and my endeavours to carry 

 out the suggestions of the Committee, which they were so good as to make 

 in connexion with my letter of 13 Feb. 1866, were reluctantly deferred 

 to the ensuing October, when a clear atmosphere might again be expected. 



VOL. XIX. B 



