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S. Zanotti, in order to determine the place of Ve- 
nus on the Sun, made ufe of a quadrant of 24 feet 
radius, in the telefcope of which were placed two 
wires, the one in an horizontal, the other in a vettical 
direction : by obferving the appulfes of the limbs of 
the Sun and Venus to thefe wires, fuccefiively, no 
error from refradtion can take place. But it is of no 
fmall confequence to the accuracy of thefe obferva- 
tions, that the wires fhould be placed truly perpen- 
dicular to each other. For this purpofe, the quadrant 
was placed in the plane of the meridian, and a ftar, 
during its tranfit, was obferved more than once, ac- 
curately to run along the horizontal wire. Though 
the polition of the vertical wire was often tried by 
terreftrial objedts, yet other methods of examination 
were made ufe of. At the fame altitude, both before 
and after noon, the paffage of the Sun not only over 
the horizontal, but alfo over the vertical wire, was 
obferved, that it might from thence appear, whether 
the times of paffage, when the neceffary errors in ob- 
ferving are allowed for, were equal in both cafes. In 
each of the following obfervations, the altitude is not 
nicely determined; becaufe an error of one degree 
would occafion little or no difference in the quantity of 
the parallax. 
The obfervations, fourteen in number, as given by 
the author, follow : 
Obfervation ift. Altitude 5 0 14'. 
16 ^4 o s preceding limb at the horizontal wire. 
^4 o s preceding limb at the vertical wire. 
15 ? *s preceding limb at the vertical wire. 
