160 EEPORT — 1891. 



The cell thus set up may be mounted in any desirable manner. It is 

 convenient to arrange the mounting so that the cell may be immersed in 

 a water bath up to the level of, say, the upper surface of the cork. Its 

 temperature can then be determined more accurately than is possible 

 ■when the cell is in air. 



Interim Report of the Committee, consisting of Professor Cayley, 

 Professor Sylvester, Mr. A. K. Forsyth, and Professor A. Lodge 

 (Secretary), appointed for the purpose of carrying on the 

 Tables connected ivith the Pellian Equation from the point 

 where the ivork ivas left by Degen in 1817. 



A LASGE part but not the whole of the work has been completed, but the 

 Committee hope to have it completed in time for next year's meeting of 

 the Association. 



lOL of the grant of 15L has been expended. 



Seventh Report of the Committee, consisting of Sir G. Gr. Stokes 

 (Chairman), JProfessor Schuster, Mr. Gr. Johnstone Stonet, Sir 

 H. E. Koscoe, Captain Abney, Mr. Whipple, Professor McLeod, 

 and Mr. Gr. J. Symons (Secretary), appointed for the purpose 

 of considering the best methods of recording the direct Intensity 

 of Solar Radiation. 



Your Committee have to report that, after considerable search, Professor 

 Schuster found the thermometers constructed for Professor Balfour 

 Stewart for use with the apparatus designed by and constructed for 

 him, and that the apparatus and a mass of correspondence relating thereto 

 had been placed in Professor McLeod's hands. He reports that he has 

 tested all the thermometers, and made observations with the instrument 

 when opportunity has offered. He has found it desirable to provide a 

 screen to prevent the action of the sun on the outside of the instrument 

 affecting too much, or too unequally, the reading of the internal thermo- 

 meters. It was always contemplated that the action of the sun on the 

 case of the instrument would affect the embedded thermometers ; but as 

 care was taken that the central thermometer should be prompt in respond- 

 ing to changes of temperature, while the embedded thermometers, in 

 consequence of the way in which they were protected, should change but 

 elowly, it was expected that the difference between the temperatures 

 marked by the central thermometer and by the embedded thermometer 

 respectively would be sensibly proportional to the intensity of solar 

 radiation, notwithstanding the changes of temperature of the outer case. 

 This anticipation, the correctness of which is of vital importance to the 

 success of the instrument, has not, however, as yet been tested experi- 

 mentally, and the trials would require to be made under specially favour- 

 able atmospheric conditions. The Committee hope to report definitely 

 in the course of another year as to the utility of the apparatus and 

 desire reappointment without any grant. 



