: 'ey? I 
zing cavity, from the fur face downwards, whofe 
other dimenfiohs were of much greater extent. 
Being thus perfwaded of the depreffion of this 
great fpot below the furface, I immediately fet a- 
bout examining {mailer ones, in order to difeover 
if they were of the fame kind. With this view, I 
Began a courfe of obfervations, that from them I 
might either make the inference univerfal, or limit 
it, as the pheenomena fhould point out. I was not 
long engaged in this purfuit, before I perceived in 
them the fame changes of their umbras, which 
have been deferibed above at fo much length. This 
was manifeft in fpots of any confiderable fize, when 
the air was favourable, and the telefcope well ad- 
jufted for diftindt vifion. The firft, which I faw 
undergo this change upon its near approach to the 
limb, was onjanuary 17th, 1770, as reprefented in 
Fig. 1. [Tab. II.] The figures 2, 3, 4, in this plate, 
and 1, 2, 3, 4, [Tab. III.] are fo many other in- 
fiances taken from the regiffer of the obfervations 
at that time. But, as this appearance, of the umbra 
changing, is evident from a bare infpedtion of the 
figures, w r e have omitted any unnecelfary deferip- 
tion of them. Thefe eight cafes are taken out 
from above 40 others of the fame kind ; and in them 
all, the nuclei were in the middle of the umbras, 
before their approach to the limb. It may be re- 
marked, that in fig. 2. [Tab. II.] the fame fpot c 
traverfed the difc.and had its umbra changed, both 
in the coming on and going off. In general, we have 
found that the umbra thus changes, when a fpot is 
about a minute did ant from the. limb, at a medium. 
From 
