1 74 On the Satellites and Belts of Jupiter.. 



directly under this aperture, draw several concentric semi- 

 circles, and fix the meridian line according to the preceding 

 directions. The gnomon should have several other holes made 

 through it in a line perpendicular to the horizon, that the 

 sun's rays at noon, flowing through some of them, may fall 

 near the north end of the stone at all seasons of the year ; 

 for if only one hole he used, the sun's image will fall near 

 the centre of the gnomon in the summer, and in the winter 

 it will be thrown far beyond the north end of the stone. 

 I am, sir, your humble servant, 



Ez. Walker. 



XXVIII. On the Satellites and Belts of Jupiter. By 

 Mr. John Snart. 



To Mr. Tilloch. London, 



_ SIR, July 18, 180S. 



J. he salutary effects of the most tempestuous weather are 

 so obvious that most persons have observed them, and what- 

 ever disagreeable effects we may encounter while these august 

 operations are going on, we are fully compensated for in the 

 issue. 



Friday last (llth instant) was a very tempestuous day: 

 however, about ten o'clock P. M., after our atmosphere 

 was pretty much attenuated by the discharge of vast quan- 

 tities of rain, much thunder, lightning, &c.j and Jupiter 

 being retrograde in longitude 9 s 1° 21', i. e. in 1° 21' of 

 Capricorn, right ascension 272°, and consequently in that 

 part of the heavens which is about south-south-east of Lon- 

 don, my attention was called, by an acquaintance of mine, 

 to a sight which afforded me a great deal of pleasure, viz. 

 " a view of the third and fourth satellite of Jupiter by the 

 naked eye. But though professor Beauchamp, I think, was 

 so remarkable for the singular acuteness of his vision, that 

 he could discern these auxiliaries by his natural optics, I was 

 apprehensive that I might be deluded by some stars of the 

 7th or 8th degree of magnitude. Therefore, to prove the 

 identity of. these secondary planets, I took a good night te- 

 lescope to examine the primary and its-satellites, as well as 



to 



