48 Dr. Herschel on the Nature and Construction 
swimming in the fluid matter of the sun ; dipping down occa- 
sionally. 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 li- 
quid, 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 bo- 
dies of such comets as draw very near to it has been assigned. 
The bright spots, or facuke, 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 un- 
less by reflection ; though the proofs, which are brought in 
support of that opinion, seem to me 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 pre- 
sent time ; who have furnished us with materials for exami- 
nation. 
In supporting the ideas I shall propose in this paper, with 
regard to the physical construction of the sun, I have availed 
myself of the labours of all these astronomers, but have been 
induced thereto only by my own actual observation of the 
solar phenomena ; which, besides verifying those particulars 
that had been already observed, gave me such views of the 
