cf 'Doubfe 'Stars. 8^ 
111. 108. Fl. i Aqfiilae prsecedens ad boream. 
July 7, Double. Above f n. preceding the 19th, 111 a line 
378 3. parallel to (3 and f Aquilae. Very unequal. L. r. ; 
S. dr. Diftance 12" 5s 777 .. Portion 5B 0 2j y f. fol- 
lowing. 
309. Fl. ip 3 " 1 Aquilae praecedens ad Boream 1 . 
July 7, Double. About if degree n. preceding the 1 9th , hi 
1783. aline parallel toe and ^ Aquilae. Pretty unequal. Both 
rw. Distance io 77 I 3 777 . Portion 22 0 6' n. preceding, 
no. Fl, 77 s Cygni borealior et praecedens. 
Sept. 17, Quadruple. Full f degree 11. preceding the 17th, in 
3783. a line parallel to <r and » Cygni; a fmall Bar. The 
two neareft extremely unequal. L. r. ; S. d. Diftance 
with 625, 13 77 54 /7/ . Pofition 67° 36' f. following. 
The two larged; a very little unequal. Both r. Dif* 
tance with 278, 2 5 77 58 /7/ . Polition 40°" 33' 11. fol- 
and low obfervations, is evident from fome meafures I have taken to afcertain its 
quantity. Thus I found. May 4, 1783, that the perpendicular diameter of e, 
Flamsteed’s 20th Sagittarii, meafured 16" 9"', while the horizontal was 8"35' // ; 
which gives 7" 34"' for the prifmatic effect : the meafures were taken with 460, 
near the meridian, and the air remarkably clear. And though this power, which 
depends on the obliquity of the incident ray, diminilhes very fall: in greater alti- 
tudes, yet I have found its effects perceivable as high, not only as or y Corvi in 
the meridian, but up to Spica Virginis, and even to Regulus. Experiments on 
thefe two latter Ears I made November 20, 1782; when Regulus, at the altitude 
of 49°, fhewed the purple rather fuller at the bottom of the field of view than 
when it was at the upper edge ; which Ihews that the prifmatic powers of the edges 
of the eye lens were affifted in one lituation by the power of the atmofphere, but 
counteracted by it in the other, I turned the eye lens in all fituations, to convince 
myfelf that it was not in fault. This experiment explains alfo, why a ftar is not 
always beft in the center of the field of view ; a tadt I have often noticed before I 
knew the caufe. 
V©l. LXXVo Nv 
lowing. 
