VOL. LXXXV.J PHILOSOPHICAL TRANSACTIONS. 4/9 



Bradley has assigned the velocity of the solar light with a degree of precision ex- 

 ceeding our utmost expectation. Galileo, Scheiner, Hevelius, Cassini, and 

 others, have ascertained the rotation of the sun on its axis, and determined the 

 position of its equator. By means of the transit of Venus over the sun's disc, 

 mathematicians have calculated its distance from the earth ; its real diameter and 

 magnitude ; the density of the matter of which it is composed ; and the fall of 

 heavy bodies on its surface. From the particulars here enumerated, it is obvious 

 tiiat we have already a very clear idea of the vast importance, and powerful in- 

 fluence of the sun, on its planetary system. And if we add to tliis the beneficent 

 effects we feel on this globe from the diffusion of the solar rays ; and consider 

 that, by well traced analogies, the same effects have been proved to take place on 

 other planets of this system ; I should not wonder if we were induced to think, 

 that nothing remained to be added in order to complete our knowledge : and yet 

 it will not be difficult to show that we are still very ignorant, at least with regard 

 to the internal construction of the sun. The various conjectures, which have 

 been formed on this subject, are evident marks of the uncertainty under which we 

 have hitherto laboured. 



The dark spots in the sun, for instance, have been supposed to be solid bodies 

 revolving very near its surface. They have been conjectured to be the smoke 

 of volcanos, or the scum floating on an ocean of fluid matter. They have also 

 been taken for clouds. They were explained to be opaque masses, swimming in 

 the fluid matter of the sun ; dipping down occasionally. It has been supposed 

 that a fiery liquid surrounded the sun, and that, by its ebbing and flowing, the 

 highest parts of it were occasionally uncovered, and appeared under the shape of 

 dark spots; and that, by the return of this fiery liquid, they were again covered, 

 and in that manner successively assumed different phases. The sun itself has 

 been called a globe of fire, though perhaps metaphorically. The waste it would 

 undergo by a gradual consumption, on the supposition of its being ignited, has 

 been ingeniously calculated. And in the same point of view, its immense power 

 of heating the bodies of such comets as draw very near to it has been assigned. 



The bright spots, or faculae, have been called clouds of light, and luminous 

 vapours. The light of the sun itself has been supposed to be directly invisible, 

 and not to be perceived unless by reflection; though the proofs, which are 

 brought in support of that opinion, seem to amount to no more than what is 

 sufficiently evident, that we cannot see when rays of light do not enter the eye. 

 But it is time to profit by the many valuable observations that we are now in 

 possession of. A list of successive eminent astronomers may be named, from 

 Galileo down to the present time, who have furnished us with materials for ex- 

 amination. 



In supporting the ideas proposed in this paper, with regard to the physical con- 



