Magnitude of the Georgium Sidus, &c. 1 1 
It appears then, from thefe experiments, that the power of 
the telefcope has not been over-rated ; and that, therefore, the 
meafures of the Georgium Sidus cannot be found too fmall on 
that account. 
There is one caufe of inaccuracy or deception in very fmall 
meafures, long fufpedled, but never yet Sufficiently invefti- 
gated. That there is a di/perjion of the rays of light in their 
paflage through the atmofphere, we may admit from various 
experiments ; if then the quantity of this difperfion be, in ge- 
neral, regulated by certain difpofitions of the air, and other 
caufes, it will follow, that a concentration may alfo take place : 
for fhould the rays of light, at any time, be lefs difperfed than 
ufual, they might with as much reafon be faid to be concen- 
trated, as the mercury of a thermometer is faid to be contrafled 
by cold, when it falls below the zero. 
061. 12, i y 8 2. The night was fo fine, that I faw the Geor- 
gium Sidus very plainly with my naked eye. I took a meafure 
of its diameter by the lucid difk, and found, that I was obliged 
to come nearer, as the Planet rofe higher, and gained more dif- 
tin6t light. At the altitude of 5 z° it was as follows : 
3,415 
73 1 > 3 
,0046698 ; 
and 
227 
061. 13, 1782. i6h. I viewed the Georgium Sidus with 
feveral powers. With 227 it was beautiful. Still better with 
278. With 460, after looking fome time, very diftinct. I 
perceived no flattening of the polar regions, to denote a diurnal 
motion ; though, I believe, if it had had as much as Jupiter, 
I fhould have feen it. With 625 pretty well defined. 
061. 19, 1782. The inconvenience arifing from the quan- 
tity of light contained in the lucid difk, fuggefled to me the 
C 2 idea 
