270 Dr . Herschel's Observations to investigate 
OF OPENINGS. 
Openings are Places where the luminous Clouds of the Sun are 
removed . 
That thoser appearances which have been called spots in the 
sun, are real openings in the luminous clouds of the solar atmo- 
sphere, may be concluded from the following observations, 
where the sides or thicknesses of the borders which limit the 
openings are distinctly described. 
Jan. 4, 1801. There is a large opening much past the centre 
of the sun, with a shallow about it. * On the preceding side, I 
see the thickness of the shallow, from its surface downwards. 
On the following side, I also see the edge of the shallow near 
the opening ; but it is sharp, and its thickness cannot be seen. 
I see also the side of the elevation surrounding the shallow, 
going curvedly down to the surface of the shallow, on its pre- 
ceding side. 
A large collection of openings, of very different sizes, are near 
the following limb. They all manifest the same kind of optical 
appearance, but on the side which is contrary to that in the open- 
ing before mentioned ; for here the thicknesses or depths of the 
shallows, and of the slopes going down from the upper surface 
to the shallows, are only visible on the following side, but not 
on the preceding one.-f 
* See Plate XVIII. Fig. 1 and 2. 
f For a geometrical proof of the depression of the nucleus of a spot, as an opening 
was formerly called, see a most valuable paper of Observations on the Solar Spots, 
by the late Alexander Wilson, M. D. Professor of Practical Astronomy in the 
University of Glasgow. Phil. Trans. Vol. LXIV. Part I. 
