i4J* Yunnel beneath t^e Thamn.—'Six SateHties of the Georgium Stdus, 



I do not find, from the enquiries I have yet been able to make, that any effective fteps have 

 been taken towards carrying this plan into execution. It may, as Mr. D. obferves, be done 

 either at the expence of the two counties, or by a private fharing company under an aft of 

 Parliament of the fame tenor as is ufually obtained for canals. But whatever may be the 

 mode, there can be no doubt of the very great commercial advantages of fuch a communi- 

 cation. It would demand a greater degree of attention and refearch into the circumftances 

 of local fituation ; fuch as the depth and pofition of the main channel, the elevations of the 

 banks, the nature of the ground, with the prices of materials and workmanfliip, than on the 

 prefent occaiion can be thought of, to form any judgment of the eftimate or the difficulties 

 which may attend this important work. To the great public, Mr. Dodd's propofal will ap- 

 pear interefting in a more general point of view. Wnen it is confidered that the praiTtice of 

 making tunnels has now been known for a confiderabie number of years in this king- 

 dom ; that in many, if not moft inftances, a tunnel will be much cheaper, and full as fafe, 

 durable and convenient as a bridge ; that the tunnel may be made (at leaft in favourable cir- 

 cumftances of the ground) in fituations where a bridge would be impra£ticab'ie, and will leave 

 that moft valuable defideratum the clear navigation above unimpeded : — this happy thought 

 of Mfr Dodd may be allowed topromife beneficial confequences of the greateft magnitude to 

 the community. 



Dr. Herschel has difcovered four additional fatellites of the Georgium Sidus. His paper 

 on this obje£t is inlerted in the late publication of the Royal Society *. By recurring to his- 

 former communication on this fubjeift fj the two old fatellites are found to revolve, the firfi; 

 in 8 days 17 h. i m. 17 iec. at the diftance of 33'' from its primary, and the fecondin 13 d. 11 h. 

 j m. 1,5 fee. at the diftance of 44''',23. The planes of their orbits form fuch large angles with 

 that of the planet itfelf, and confequently to the ecliptic, as to be almoft perpendicular to it. 

 - To this remarkable departure from the analogy of the old planets another ftill more fingular 

 is now announced. They movi in a retrograde dlreBion ! The new fatellites revolve as follows^ 

 the periodical times being inferred from their greateft elongations : The interior fatellite in 

 5.d. 21 h. 35 m. at the diftance of 25",S. — A fatellite intermediate between the two old 

 bnes in lod. 23 h. 4 m. at the diftance of 38'',57. — The neareft exterior fatellite at about 

 double the diftance of the fartheft old one, and confequently its periodical time 38 d. i h, 

 4p;m. — And the moft diftant fatellite full four times as far from its primary as the old fecond 

 fatellite. Whence it will take at leaft 107 d. 16 h. 40 m. to complete its revolution. Whether 

 the motions of thefe four be direct or retrograde, is, I fuppofe, not yet determined. 



From fome obfervations of the Do£tor, with an excellent feven foot teletcope, certain appear- 

 ances refcmbling that of two rings furrounding the planet, and croffing each other at right 

 angles, were feen on feveral different days. They were not altered in pofition by turning the 

 fpeculum in its cell ; but there is little doubt that they were optical deceptions, becaufe theV' 

 kept their pofition with refpeci to the tube, after the relative pofition of the parallel had been 

 much changed by the earth's rotation, and becaufe they did not appear with larger telefcopes 

 applied during the courfe of ten years. The difk of the Georgium Sidus is flattened. It there- 

 fore revolves with confiderabie rapidity on its axis. From the very faint light of the fatellites, 

 they are obferved to difappear in thofe jwirts of their orbits which bring them apparently neareft- 

 the planet. This does not arife from an atmofphere j for theefteCt is- the fame, whether tise; 

 jbtcUite be withiji or beyond the planet. 



• Phil. Tranf. 178S, p. 47. f Ibid. 178?. 



