a 5^ K be Zach’s Agronomical Objemnikm* 
* * ^w^ ^qBaagg roanTW ^ > 
, .... : >. ' :': ' ' ;■ ; \ T.,J t <i\Ui ' ' -V It 1 , 3, *. 1 i A , 
I only add an important remark upon the diameter of Mer- 
cury, which the aflronomers fuppofed in this tranfit — iz" . 
Let ABC reprefent the fun’s difk ; in P an external in Q^an 
internal contad ; ANC the apparent path of Mercury over the 
fun. 
The femi-diameter of the funr: 9 jz", this of Mercury in our 
fuppofition = 6 // , MN“942 a/ the lead diftances of the centers. 
In the right-angled triangle MNP it is MP 972" 4- 6 /x =: 978^, 
MQ — 972" — 6 A/ — 966" ; therefore NP will be found ^260^ 
and NQ= 2 i o" : now NP — NQ= PQp=: 50", which converted 
into time gives 8' i\" for the time the diameter of Mercury em- 
ployed to run over the limb of the fun ; but by the obfervations 
of M. Wallot I find this time conftantly in both contadls 
5' 3.5"; therefore 8 7 14" : 12" 5' 35" : 8", 137, which 
fhould be the diameter of Mercury ; and indeed M. Wallot, 
by an immediate meaflire, taken with an excellent wire-micro- 
meter, finds this apparent diameter not greater than 9", which 
fufficiently thews that this diameter fuppofed 7" in the mean 
diflance is alfo too great. 
I am, &c. 
