J O-USrM-A L. 



OF 



NATURAL PHILOSOPHY, CHEMISTRY, 



AND 



'fli'k "-Amc 



APRIL, 1804.. 



ARTICLE I. 



'..,■■ : ' ^ )' t ^■, ■ > " ; ^^ 



Experiment proving the Advantage of Perifcopic SpeSlacles. Coni'- 



municated in a Letter from W. H. Wollaston, M. D. 



F.R.S. 



. ToMr.NZCHOLSON. 



SIR, • ■ '■ : - " 



JL HE opinion given by Mr. Jones, in your laft Journal, re* Mr. Jones's 

 fpefling the improved form of fpedacle-glafles, on which I had improved fpec- 

 delivered my fentinients in the number preceding (p. 144,) in- tacle glaffes, 

 duces me to addrefs you once more upon that fubjedt. 



It appears wholly uhneceflary to follow Mr. J. through his referred to ex- 

 various obfervations, or to remark upon the experiment by " 

 which hedecfciveshimfelf; becaufe all doubt of the advantage 

 of the perifcopic glaflTes may be removed by the follovving 

 dired comparative trial, which any perfon vyho choofes can 

 make without difficulty. 



' -I have before me two gl^fTes, eath of four inches " pofitive With tht form 

 focus," as propofed by Mr. J. the one double-convex, which ^^^gnded by Mr". 

 i^i his judgment is pronounced to be " indubitably the bejl and Jones, 

 'inoji convenient that can be devifed*' (p* 194) ; the other a con- 

 'tavo-convex, or menifcus^. which he thinks "evidently the 

 •ivor/t of the tzvo for afpedUtckr^gh/s," (p. 197*) 



When I fix the former at the diftance for moft diftin£t vifion the extent of ' 

 ;Oppofite to a printed oaavo page, and approach my eye to the cimpwed'with 

 ' Vol. \ai.-~ApRiL, 1804, R gMs, that by th* 



