Invention of Achromatic Glaffes. 177 
cumftance, we fupprefs the reft of his paper, and fubjoin an article on the 
fubjeét which appeared in the Gentleman’s Magazine for October 1790» 
and which, we have been informed by Mr, Ramfden, contains. a true ftate- 
ment of thefaéts, == ®t 
_ The inventor was Chefter More Hall, Efq. of More Hall, in Effex, who 
about 1729, as appears by his papers, confidering the different humouss of 
the eye, imagined they were placed fo as to correét the different refrangibi- 
lity of light. He then conceived, that if he could find fubftances having 
fuch properties as he fuppofed thefe humours might poffefs, he fhould be 
enabled to conftruct an object- glafs that would fhow objects colourlefs. 
After many experiments, he had the good fortune to, find thefe properties 
in two different forts of glafs; and by forming lenfes made with fuch glafs, 
and making them difperfe the rays of light in contrary direétions, he fuc- 
ceeded. About 1733 he completed feveral achromatic objet glaffes 
(though he did not give them that name) which bore an aperture of more 
than 22 inches, though the focal length did not exceed 20 inches ; one 
of which is now in the poffetlion of the Rev. Mr. Smith, of Charlottes 
ftreet, Rathbone-place. This glafs has been examined by feveral gentle- 
men. of eminence and feientific abilities, and found to poffefs the properties 
of the prefent achromatic glaffes. 
«Mr. Hall ufed to employ working opticians to grind his lentes; at the 
fame time he furnifhed them with the radii of the furfaces, not only to 
correét the different refrangibility of rays, but alfo the aberration arifing 
from the fpherical figures of lenfes. Old Mr. Bafs,who at that time lived 
in Bridewell, Precinét, was one of thefe working opticians, from whom 
Mr. Hall’s invention feems to have been obtained. 
“In the trial at Weftminfter-hall about the patent for making achro- 
matic telefcopes, Mr. Hall was allowed to be the inventor; but Lord 
Mansfield obferved, that “ it was not the perfon who locked up his inven- 
tion in his {crutoire that ought to profit by a patent for fuch invention, but 
he who brought it forth for the benefit of the public.” This, perhaps, 
might be faid with fome degree of juftice, as Mr. Hall was a ‘gentleman 
of property, and did not look to any pecuniary advantage from his difco- 
very; and, confequently, it.is very probable that he might not have anin- 
tention to make it generally known at that time. 
~« That Mr. Ayfcough, optician on Ludgate-hill, was in poffeffion of 
one of Mr. Hall’s achromatic telefcopes in 17549 is a fa&t which at this 
time will not be difputed,” 
‘Vou. I. N XII. A 
