286 On Physical Observations to he undertaken in India. [Mar. 5, 



time, the direction of the wind, the character of the clouds, and any electric 

 discharges which might occur should be mentioned. 



'* In this way we should gradually obtain from independent observation 

 a map of the purely terrestrial hues. In the construction of the map much 

 must be left to the discretion of the observer, as the appearance changes 

 rapidly with the varying altitude of the sun. When constructed, the map 

 ought to be repeatedly compared with the object, with a view to determine 

 whether the system of atmospheric lines be single, or consist of two or 

 more systems superposed. Should two gases possessing the power of de- 

 finite absorption be present, as it is not likely that they would occur in the 

 same proportion on different occasions, and under different conditions of 

 weather, the complex character of the atmospheric system, if it be complex, 

 would thus probably be in time revealed. The map should also be com- 

 pared with the map drawn by Sir David Brewster and Dr. Gladstone, 

 from observations made in England and Scotland (Philosophical Transac- 

 tions for 1860). 



" § 5. In connexion with the offer made by Mr. Hennessey, the Com- 

 mittee have had under their consideration the subject of the total solar 

 eclipse of next year, which will be visible in India. As it will be long 

 before equal facilities for observing the phenomena of the totality recur, it 

 seems desirable not to lose this opportunity of making some physical ob- 

 servations on the phenomenon, which at the present time are of great in- 

 terest. Above all, the character of the spectrum of the red protuberances 

 may be expected to throw great light on their nature ; and it is therefore 

 important to be prepared with an instrument for observing their spectrum, 

 and that of the corona. It is also important that fresh observations should 

 be made on the polarization of the light of these objects. 



" In order that a sufficient apparent breadth may be given to the red 

 protuberances to permit of the convenient observation of any lines by 

 which their spectrum may be crossed, it is necessary to use a tolerably 

 high magnifying-power ; and in order that this may be done with the 

 least possible loss of light, a corresponding aperture is required in the 

 telescope to be employed. Messrs. Cooke and Sons have on hand a fine 

 telescope of 5 inches aperture, mounted as a portable equatorial, furnished 

 with clock movement, which may be obtained for a moderate sum ; and 

 the Committee recommend that this instrument be purchased, with such 

 part of the mounting as is required for the observations contemplated, and 

 be provided with a star-spectroscope. They understand that Lieutenant 

 Herschel, who is now in this country, and is going out to India in the 

 course of a few months, would be willing to undertake the observations, 

 subject to the approval of Colonel "Walker, the Director of the Great Tri- 

 gonometrical Survey of India. But as clouds might interfere with the 

 observations by the large instrument at the critical moment, the Committee 

 think it desirable that three or four direct spectroscopes, by which the 

 general character of the spectrum might be observed, should be entrusted 



