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tranfit fr©m them; and his account of the v/ork 
follows : 
Delineation of the tranfit of Venus over the Sun, accord- 
ing to the Norriton obfervations, with the principles 
of the work. By Mr, Rittenhoufe. SeeTab.XV. 
fig. 4. 
“ The Sun’s horizontal parallax is afilimed 8'', 6 5 
‘‘ at his mean diftance from the earth; from which, 
“ and the obferved lead; difiance of the centers of the 
“ Sun and Venus, the chord for the tranfit line was 
“ laid down. The femi-diameters of the Sun and 
‘‘ Venus are taken as by^the above obfervations. 
“ One point in the tranfit-line was then fixed by the 
“ firft micrometer diftance of the limbs at 3’’ / 19'' 
“ apparent time. This line was carefully divided in- 
to hours and minutes, on the fuppofition that Ve- 
“ nus moves 240^,36 over the Sun’s difk in an hour, 
“ according to a calculation I had formerly made 
“ from Halley’s Tables. The place of Venus’s cen- 
“ ter in the tranfit-line was then marked to the times 
“ of each of the micrometer obfervations, and from 
thence the apparent place of her center found, by 
“ fetting off the quantity of her parallax from the 
“ Sun in its proper diredion. About each of the 
“ centers fo found, a circle is defcribed with the rad. 
“ 28'k6, her obferved femi-diameter. Blank lines 
“ were next drawn through the Sun’s center, and the 
“ apparent place of the center of Venus. On thefe 
“ the red lines were drawn from the Sun’s limb, pre- 
“ cifely of fuch length as we found them by the mi- 
“ crometer; fo that it may be feen at once how 
“ far the micrometer meafures agree with each 
VoL. LIX. T t “ other. 
