Additional Notes, 403 



might possess, he should be enabled to construct nn ohjcct glass 

 that Mould show objects culourk'ss. After many experiments, ho 

 ImJ the good fortune to tind these properties in two ditferent 

 kinds of glass ; and by forming lenses made of such glass, and 

 making them disperse the rays of light in contrary directions, he 

 succeeded. About 1733 he completed several achromatic objLtt 

 glasses (though he did not give them this name), that bore an 

 aperture of more than two inches and a half, thou'^h tiie focal 

 length did not exceed twenty inches. One of tliesc glasses, 

 which, in 179O, was in possession of the rev. Mr. Smith, of 

 Charlotte-street, Rathbone Place, London, has been examined 

 by several gentlemen of eaiinence in tlie scientilic world, and 

 found to possess the properties of the present achromatic glasses. 



•In the trial at Westminster-Hall, about the patent for making 

 achromatic telescopes, Mr. Hall was allowed to be the inventor ; 

 but lord Mansfield observed, *' that it was not the person who 

 locked up his invention in his scrutoire that ought to profit by a 

 patent for such invention, but he who brought it fortli for th« 

 benefit of the public." 



That Mr. Ayscough, optician, on Ludgate-Hill, was in pos- 

 session of one of Mr. Hall's achromatic telescopes in 17•'5-^, is a 

 fact indisputable. — Gcnthman's Magazine, vol. Ix, part ii, for 

 1790, p. 890, 8:c. 



Note (P), p. 75. — Since the close of the eightcentli century 

 tu:o neiv planets have been discovered. The first was discovered 

 January 1, 1801, by Mr. Piazzi, of Palermo, in Sicily. It is called 

 by the discoverer Ceres, but by his brother astronomers Viazzi. 

 The second was discovered on the 28th of March, 1802, by 

 Dr. Olbers, of Bremen, and is called by him Pallas, but others 

 give it the name of Others. 



The planet Piazzi {or Ceres) revohes bet\\'een Mars and Ju- 

 piter. It is not, apparently, larger than a fixed star of the eighth 

 magnitude. The inclination of its orbit to the plane of the eclip- 

 tic is about 10 deg. 3t? min. 57 sec, and the time of its periodical 

 revolution is four years, seven months, and ten days. 



The planet Olbtrs (or Pallas) also revolves in tiie wide space 

 between Mars and Jupiter. It differs very little in ai)pearance 

 ^fi-om stars of the eighth magnitude. The inclination of its orbit 

 to the plane of the ecliptic is 35 deg., n \ery extraordinary' degree 

 of obliquity, which shows that the ZoJiac must be cons-iderably 

 enlarged, if we continue to distin^uiih by that name the /one tu 



2 D i 



