161 ] 
of i ".3 nearly ; that is, in cafe the interval between 
the obfervations was eight hours, and Mars at his 
mean diffance ; but if Mars was not at his neareft 
diffance, this change would in the fame time amount 
to i " . 7 nearly. In like manner, if a tranfit of Venus 
happens near the new or full Moon (as will be the 
cale next year), the time of the tranfit will be affedted 
by a change of place, fuch as the Earth’s center will 
defcribe in its epicycle, during the time of the whole 
tranfit, if the beginning and end are obfervedin the fame 
place ; or during the difference of abfolute time, at 
which the tranfit appears to begin or end to different 
obfervers in diftant meridians. Thus, when the fame 
oblerver fees the beginning and end in the fame place, 
the bale defcribed by that obferver, from the Earth's 
diurnal motion, muff be corredfed by the fpace de- 
fcribed by the Earth’s center, in the circumference of 
it’s epicycle, during that time ; which, if it be fup- 
pofed of feven hours, will amount to an angle of 
I feen from Venus: but, where the beginning 
or end is feen by different obfervers in diffant meri- 
dians, as the difference of abfolute time can hardly 
amount to above 15 minutes, the change of place of 
the Earth’s center will for that time be but fmall ; 
however, at the rate beforementioned, it will for 1 5 
minutes affedt the paralladtic angle feen from Venus, 
by about of a fecond ; and the parallax of the 
Sun, by about part of the whole : but this pro- 
portional part will remain the fame, whether the 
diftance of meridians be fuch as produce a greater or 
Jefs difference of abfolute time than 1 5 minutes *. 
* If an error of part of the whole may be fuppofed in 
the obfervation for determining the Sun’s parallax by the tranfit' 
Vol. LVIII. Y From 
I 
