231' Queries 7-cspccti7ig the Discovcri/ of AchromaticTelcscopcs. 



'* About 1733 he completed several achromatic object- 

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

 an aperture of 2\ inches, though the focal length did not 

 exceed 20 inches ; one of which is now in the possession of 

 the Rev. Mr. Smith of Charlotte-street, Rathbone Place. 

 This glass has been examined by several gentlemen of emi- 

 nence and scientific abilities, and found to possess the pro- 

 perties of the present achromatic glasses. 



" Mr. Hall used to employ working opticians to grind his 

 lenses ; at the same time he furnished them with the radii 

 of surfaces, not only to correct the different refrangibility of 

 the rays, but also the aberration arising from the spherical 

 figures of lenses. Old Mr. Bass, who at that time lived in 

 Bridewell precinct, was one of these working opticians, from 

 whom Mr. Hall's invention seems to have been obtained. 



" In the trial at Westminster Hall about the patent for 

 making achromatic telescopes, Mr. Hall was allowed to be 

 the inventor ; but Loixl 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 forth for the benefit of the public' This might per- 

 haps be said with some degree of justice, as Mr. Hall was a 

 gentleman of property, and did not look to any pecuniary ad- 

 vantage at the time from his discovery. That Mr. Ayscough, 

 optician on Ludgate Hill, was in possession of one of Mr. Hall's 

 telescopes in 1754, is a fact which at this time will not be dis- 

 puted." 



The note, of which the substance is here given from the 

 Philosophical Magazine for November 1798, vol. ii. p. 177, is 

 there stated to be taken from the Gentleman's Magazine for 

 October 1790; but it derives particular interest from Mr. Til- 

 loch's information, that the celebrated optician Mr. Ramsden 

 confirmed the truth of the statement. 



Are any of Mr. Hall's achromatic telescopes now in ex- 

 istence ? 



Is any correct information now to be obtained respecting 

 the performance of Mr. Hall's telescopes ? 



Are any of Mr. Hall's papers containing the principles 

 of his discovery extant? 



Is any information to be obtained from records of the trial 

 in Westminster Hall, respecting the original discovery of 

 achromatic telescopes ? 



Is any thing further known respecting the philosophical 

 labours or the life of Mr. Hall ? 



These inquiries are, I conceive, not undeserving the atten- 

 tion of the Astronomical Society. Florence preserves with rcli- 



ffious 



