406 Col. Beaufoy's Astronomical Observations. [June, 



his photometer with the measurements obtained by Bouguer 

 from a comparison of illuminating effects, and conceives the 

 result completely favourable to the accuracy of his instrument. 

 (See Leslie on Heat, Chap. 20.) 



With respect to the theory deduced from these and kindred 

 phenomena by that distinguished philosopher, it cannot but 

 excite admiration for its simplicity, and the readiness with which 

 it explains the phenomena ; but it surely cannot be considered 

 as proved, that because light has the power of exciting or com- 

 municating heat in those bodies on which it impinges, that the 

 light is, therefore, transformed into heat ; and after all, the mode 

 in which this transformation is effected in the " igneous fluid " 

 still remains to be accounted for. 



Towards ascertaining the nature of the heating power thus 

 excited in the solar rays, one important step seems to me to be 

 involved in the question whether the heating power does always, 

 and especially at high intensities, increase precisely in propor- 

 tion to the intensity of light, or number of rays impinging upon, 

 or absorbed by, a given surface. 



The want of a photometer on the principle of illumination, 

 and that essential difficulty, the want of a standard for compa- 

 rison, are great obstacles in the prosecution of such an inquiry. 

 I have, however, attempted it by adopting other means in which 

 these difficulties seem to me to be got rid of. As, however, the 

 detail of these experiments will occupy some space, I must 

 reserve them for a future opportunity. 



Article II. 



Astronomical Observations, 1824. 

 By Col. Bcaufoy,' FRS. 



Bushei/ Heath, near Stanmore. 



Latitude 51° 3T 44-3" North. Longitude West in time 1' 20-93". 



April 14. Immersion of Jupiter's third < 9 h 19' 30" Mean Time at Bushey. 



satellite ( 9 20 51 Mean Time at Greenwich. 



April 30." Emersion of Jupiter's first C 10 25 00 Mean Time at Bushey. 



satellite ^ 10 26 21 Mean Time at Greenwich. 



* Jupiter's limb very tremulous. 



