PORTION OF THE COSMOS. THE PLANETS. 387 



taut from the 1st 3'6 ; the 3d from the 2d 5'7 ; and the 

 4th from the 3d 11 '6 semi-diameters of Jupiter. Pries and 

 Challis have attempted to shew that the so-called law of 

 Titius prevails in all the systems of satellites, even in that 

 of Uranus ( 631 ). 



Uranus. 



The recognition of the existence of this planet, the great dis- 

 covery of William Herschel, not only augmented for the first 

 time the number of those six planets which had for thousands 

 of years been known to man, and more than doubled the dia- 

 meter of the solar domain ; it also led, at the end of 65 years, 

 by means of the perturbations sustained by Uranus proceeding 

 from still more distant regions, to the discovery of Neptune. 

 Uranus was discovered accidentally (March 13, 1781) 

 during the examination of a small group of stars in Gemini, 

 and was recognised by means of its minute disk, which, 

 under the successive employment of magnifying powers of 

 460 and 932, increased much more than did other stars in 

 its vicinity. The keen-sighted and sagacious discoverer, so 

 familiar with all optical phsenomena, also remarked, that 

 with increased magnifying powers the intensity of light in 

 the new body decreased considerably ; whilst in fixed stars 

 of equal magnitude (between the 6th and 7th) it remained 

 the same. 



Herschel termed Uranus, when he first announced its 

 existence ( 632 ), a comet ; and the united labours of Saxon, 

 Lexell, Laplace, and Mechain, which were greatly facilitated 

 by the discovery made by the meritorious Bode, in 1784, 

 of older observations of that body by Tobias Mayer, in 1756, 



