Magnitude of the Georgium Sidus. p 
The diflance of the luminous circle from the eye (which 1 
always meafure with deal rods) was 588,25 inches. The circle 
meafured 2,35 inches. Hence we have the angle i f 44"; 
which, divided by the power 227, gives 3", 63 for the diameter 
of the Planet. I lufpedted fome little fallacy from the want of 
a perfect refemblance in the light and colour of the artificial 
dilk to the real appearance of the Planet. 
Oft. 4, 1782. I meafured the diameter of the Georgium 
Sidus again, by an improvement in my apparatus, for I now 
ufed pale blue papers, both oiled and plain, in (lead of white ; by 
which means I obtained a refemblance of colours ; and by an 
afl'ortment of one oiled and two dry papers with two lamps 
burning, I effected the fame degree of light which the Planet 
had, and both figures were equally well defined. By firft 
changing the dilk, and, when I had one which came nearest, 
changing my diltance, I came at a perfect equality be- 
tween the Planet and dilk. The meafure was feveral times 
repeated with great precaution. The refult was 6 ~— = 
,0040283 ; and — 3^, 67. If any thing be wanting to 
the perfection of this meafure, it is perhaps that the Sidus 
fhould be in the meridian, in order to have all the advantages 
of light and diftinflnefs. 
Off. 10, 1782. The meafures of the Planet by the lucid 
dilk micrometer appearing to me very fmall, I relolved to afcer- 
tain the power of my telefcope again molt lcrupuloufy, by an 
actual experiment, without any deduction from other princi- 
ples. O11 a moft convenient and level plain I viewed two flips 
of white paper, and meafured their images upon a wall. The 
diftances were meafured by deal rods, every repetition whereof 
Vol. LXXIII. * C 
was 
