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XL VII. A Letter fro7n Richard Price, 
D. D. F. R. S. to Benjamin Franklin, 
L L. D. F. R. S. on the FffeSt of the 
Aberration of Light on the \ Time of a 
Lranfit of Venus over the Sun. 
Dear 
Read Dec. 20 
1770. 
I 
IR, 
Cannot doubt but that the obfervation 
made by your ingenious friend in the 
paper * you lent me is right. The aberration of Venus 
muft, I think, affedt the phafes of a tranfit, by re- 
tarding them, and not by accelerating them. This 
retardation is 554." j for that is the time nearly which 
Venus, during a tranfit, takes to move over 3 ".y. This, 
however, is by no means the whole retardation of a 
tranfit occafioned by aberration. There is a retar- 
dation arifing from the aberration of the Sun, as well 
as from that of Venus. The aberration of the Sun, it 
is well known, leflens its longitude about 20". and 
the aberration of Venus, agreeably to your friend’s 
demonftration, increafes its longitude at the time of a 
tranfit 3 " .y. Venus, therefore, and the Sun, at the 
inftant of the true beginning of a tranfit, muft be 
feparated from one another by aberration 23". 7 ; and, 
fince Venus then moves nearly at the rate of 4' in an 
* The paper which occafioned this letter, and which is here 
referred to, may be found in p. 358 of this volume. 
hour, 
7 
