the two lately discovered celestial Bodies . 215 
shall not under-rate the size of the star, by admitting its 
diameter to have been 45 hundredths of the lucid disk. 
The power of the telescope, very precisely ascertained, by 
terrestrial geometrical measures properly reduced to the focus 
of the mirror on the stars, was 370,42. The distance of the 
lucid disk from the eye, was 2131 inches; and its diameter 3,4 
inches. Hence we compute, that the disk was seen under an 
angle of 5' 29",09 ; and Ceres, when magnified 370 times, 
appearing, as we have shewn, 45 hundredths of that magnitude, 
its real diameter could not exceed 0A40. Had this diameter 
amounted to as much as was formerly estimated, the power of 
370 would have made it appear of 6 ' 1 o", which is more than 
the whole lucid disk. 
This extraordinary result, raised in me a suspicion, that the 
power 370 of a 7-feet telescope, and its aperture of 6,3 inches, 
might not be sufficient to shew the planet’s feeble light properly. 
I therefore adapted my 10-feet instrument to observations with 
lucid disks ; which require a different arrangement of the head 
of the telescope and finder : I also made some small transpa- 
rencies, to represent the object I intended to measure. 
April 21. The night being pretty clear, though perhaps not 
quite so proper for delicate vision as I could have wished, I 
directed my 10-feet reflector, with a magnifying power of 
516,54, also ascertained by geometrical terrestrial measures 
reduced to the focus of the instrument on celestial objects, to 
Mr. Piazzi’s star, and compared it with a lucid disk, placed at 
i486 inches from the eye, and of 1,4 inch in diameter. I varied 
the distance of the lucid disk many times ; and fixed at last on 
the above-mentioned one, as the best I could find. There was, 
however, a haziness about the star, which resembled a faint 
Ff 2 
