Ob] eft ions of M. de la land's; S<1 
examples, in which the apparent femi- diameter of the fun is 
fuppofed i6 ; , and his parallax 8". c. 
Fartheft umbra fuppofed 
Depth of nucleus in 
Apparent breadth 
to vanifti when 
dittant 
Englifti miles and in 
of 1 
neareft umbra. 
from the limb. 
l’econds. 
I. 
/ // 
I O 
-- 
// 
4.54 - 2IlS 
-* 
00 
» 
CO 
II. 
i 
o 
to 
O 
- 
3.09 - 1442 
- 
6.02 
III. 
o 15 
- 
2.09 - 975, 
- 
4.I3 
IV. 
o. 8 
-■ 
1.44 - 672 
- 
2.87 
Now, becaufe in 
every afpedt of a fpot, the real 
breadth of 
either the fartheft or neareft umbra mull be to the projected or 
apparent breadth, as radius to the fine of the angle which this 
1 refpe&ive plane makes with the vifual ray, it follows, that at 
any time before the Ipot comes lo near the limb as is exprefled 
in the above examples, the apparent breadth of the neareft and 
fartheft umbra cannot differ lo much as by the quantity there 
fet down for the apparent breadth of the neareft, when the 
other is fuppofed to vanilh. Regarding, therefore, the fartheft 
and neareft umbra of the fpot in cafe IV. as two neighbouring 
vifible objects which turn narrower by degrees as the fpot goes 
toward the limb, we Ihould undoubtedly judge ■ that they con- 
trad! as to fenfe alike, ftnee fo long as the fartheft could be 
perceived, the other cannot appear to exceed it by a quantity 
that we could diftinguilh ; and by the time the plane of the 
former coincides -with the vifual ray, the extreme nearnefs to 
the limb would prevent our forming any certain judgement of 
either. 
From this laft example, therefore, it appears manifeft that a 
fpot, anfwering to the defeription and conditions there men- 
tioned, or one a little more (hallow, would approach the limb, 
and 
