C 188 ] 
ciety, with this addition, which was originally defigned 
for that inftrument j namely, E F 
and GH, two filver wires par- 
allel to the diameter AB, and 
diftant therefrom 30° = A E — 
AG — BF — BH, the three 
parallel wires E F, A B, and 
G H, being fixed, whilft the 
moveable wires C D and I K 
opened to any angle, as ILC for intercepting the 
diameter mn of Venus, whilft CD was perpendicu- 
lar to A B, and the planet was divided into two equal 
parts by the wire E F. This micrometer was placed 
in the eye-piece of a two feet Gregorian telefcope, 
which magnified 55 times, and through the field of 
view, of which the fun pafied in 1 1 8 feconds of time. 
I had two eye-glafles to the fix feet Newtonian * 
refledtor ; one of which, being fix tenths of an inch 
focus, magnified no times ; and the other, being 
three tenths of an inch focus, magnified 220 times, 
or four times that of the Gregorian reflector. The 
greater of thefe two glafles I purpofed to truft to, 
having often experienced its fuperiority in viewing 
the occultations of Jupiter’s fatellites and the folar 
maculae. 
The. idea I had formed of the internal contadt was, 
that the planet would touch the edge of the fun in an 
inftant, like two drops of quickfilver meeting on a 
plane, and that in an inftant the black contadt would 
appear ; but in this I was deceived, the particulars of 
the phaenomenon being as follows ; viz. 
* The diameter of the great fpeculum of this telefcope was fix 
inches. 
June 
