[ *9S ] 
laft dent, approached To near to a right line. 
This led me to confider, that the fpherical ex- 
ternal angle of contad, by the fix feet telefcope, 
would be but an * eighth part of the fame angle 
by the two feet telefcope, the eye judging of 
the fame relative diftance in one telefcope as in. 
the other; and that, therefore, as the verfed 
fine of the dent in the fun's limb was but a 
fourth part as large in one telefcope as the other, 
and the laft contad vanifhed in about feconds of 
time, the laft contad might poflibly be eftimated, 
by a two feet Gregorian telefcope, about twice 
2A, or 5" or 6 /r , feconds of time later than with 
a fix feet Newtonian telefcope ; which allowance 
being made, the apparent time of the two con- 
tads, as redftced to a Gregorian refledor, mag- 
nifying 55 times : by luch a telefcope, the 
con tads at Greenwich obfervatory were, viz. 
internal contad 8 h 18' 55", external contad 
8 h 37' y" . The accounts which have been 
published of the obfervations made at Green- 
wich being, internal contad 8 h 19' o r/ , exter- 
nal contad 8 h 37' 9''; and the difference in 
each within five feconds of time, an error an- 
fwering to about a 500 th part of the fun’s di- 
ftance from the earth. 
* As the fpherical angle of contaft in the limb of Venus, and 
alfo of the fun, was four times as great in one telefcope as in the 
other, the fum of both is eight times ; which, being diminifhed 
by four times the apparent magnitude of the verfed fine of the 
leaft vifible dent in the one telefcope, what it was in the other 
telefcope, leaves the one double to that of the other. 
C c 2 XXXVI. An 
