C s6 5 3 
XIII. Observations tending to investigate the Nature of the Sun , 
in order to find the Causes or Symptoms of its variable Emission 
of Light and Heat ; with Remarks on the Use that may pos- 
sibly be drawn from Solar Observations. By William Herschel, 
L.L.D. F.R.S . 
Read April 1 6, 1801. 
On a former occasion I have shewn, that we have great reason 
to look upon the sun as a most magnificent habitable globe ; 
and, from the observations which will be related in this Paper, 
it will now be seen, that all the arguments we have used before 
are not only confirmed, but that we are encouraged to go a 
considerable step farther, in the investigation of the physical and 
planetary construction of the sun. The influence of this emi- 
nent body, on the globe we inhabit, is so great, and so widely 
diffused, that it becomes almost a duty for us to study the ope- 
rations which are carried on upon the solar surface. Since light 
and heat are so essential to our well-being, it must certainly 
be right for us to look into the source from whence they are 
derived, in order to see whether some material advantage may 
not be drawn from a thorough acquaintance with the causes 
from which they originate. 
A similar motive engaged the Egyptians formerly to study 
and watch the motions of the Nile ; and to construct instru- 
ments for measuring its rise with accuracy. They knew very 
well, that it was not in their power to add a single inch to the 
mdccci. M m 
