[ *9 3 
2. The boundary betwixt the nucleus and um- 
bra is always diftinft and well defined. Vid. 
Scheiner, p. 497. 
3. The encreafe of a fpot is gradual, the breadth 
of the nucleus and umbra dilating at the fame 
time. Vid. Scheiner, p. 491, &c. 
4. In like manner the decreafe of a fpot is 
gradual, the breadth of the nucleus and umbra 
contrafling at the fame time. Sch. p.491.498. 
5. The exterior boundary of the umbra never 
confifls of fharp angles, but is always curvilinear, 
how irregular fbever the out-line of the nucleus 
may be. Sch. 51 1. 
6. The nucleus of a fpot, whilft on the de- 
creafe, in many cafes changes its figure, by the 
umbra encroaching irregularly upon it ; infomuch 
that, in a fmall fpace of time, new encroachments 
are difcernible, whereby the boundary, betwixt the 
nucleus and umbra, is perpetually varying. Sch. 
514. Hev. 412. 
7. It often happens, by thefe encroachments, that 
the nucleus of a fpot is divided into two or more 
nuclei. Sch. 498. 
8. The nuclei of fpots vanifh fooner than the 
umbrae. Many inftances of this fort are to be 
teen in Hevelius’ plates, and the fame is affirmed 
by Mr. Derham in The PhilofophicalTranfaflions. 
9. Small umbrae are frequently feen without 
nuclei. Sch. p.497-. 
10. An umbra of any confiderable fize is feldom 
feen without a nucleus in the middle of it. Ibid. 
11. When a fpot, which confifted of a nucleus 
and umbra, is about to difappear, if it is not fuc- 
D 2 ceeded 
