Objections of M. de la lande. 
contribute to the effed, as it may do a little before its flate of 
evanefcence when fpots are very fhallow : accordingly cafes of 
this kind are perfectly agreeable to experience. This fad feems 
to have met scheiner as a flumbling-block, when he was 
intent upon bringing forward every poflible argument for the 
fpots being fbmething which projed beyond the furface. ‘ v Non. 
“ raro contrngit,” fays he, Rofa Urfina, p. 511. 44 ut magnre 
“ fobs maculae antequam ad horizontem accedant, repente ita. 
“ luce ohruantur, ut omnino videri nequeant.” 
In realoning concerning the nature of the fpots, and parti- 
cularly about their third dimenfion, the only arguments which 
are admillible, and which carry with them a perfed convidion,, 
are thole grounded upon the principles of optical projedion. 
If, lor example, by far the greater number of them be excava- 
tions, fome thoufands of miles deep, certain changes of the 
umbra would be obfervable when near the limb, as has been 
fhewn at fo much length. Were they very (hallow, or quite 
fuperficial, both fides of the umbra would as to fenfe contrad 
alike in their progrefs toward the limb : for if in cafe 4th, 
above dated, the lpot had been luppofed fuperficial, the appa- 
rent breadth of the fide of the umbra next the center of the- 
dilk, would have then been only 1T62, and that of the lide 
oppolite i 7 . 27. Now, the whole of either of thefe quantities, 
and much more their difference, would be quite infenfible. 
Again, if the nucleus extended much above the common level 
whilff the furrounding umbra was fuperficial, we Ihould 
behold manifeft indications of this by fuch an opaque body 
when feen very obliquely being projeded acrofs the fartheft' 
fide of the umbra, and by hiding the whole or part of it be- 
fore the time it would otherways difappear. According to this 
©r that condition of the fpot, fuch things mull infallibly obtain 
by 
