eS ee ee eC rl ll eee 
ee oc Mea 
* ferior to that of the different refrangibility of light; and 
“ that he has not informed us whether he had tried it.” 
In the quarto and odtavo editions of the Optics, in Doctor 
Clarke’s Latin tranflation, in Doctor Horfeley’s edition, in Mar- 
tin’s Phil. Brit. vol. III. p. 62. and in the memoir by Count Re- 
dern above referred to, the ratio of the radii is determined in 
the fame manner as defcribed above. And yet there is no doubt 
but that fome error muft have crept into the text; for the quan- 
tities KX—KIJ and R K—R J are to each other as K to R, and 
therefore the ratio of the radii, according to this expreffion, de- 
pends folely on the refraétion ‘between water and air, without in- 
volving any confideration of the refractive power of the ambient 
medium that inclofes the water, which is evidently falfe. Neither 
can it be fuppofed that Newton would have given the ratio in 
this complex form, which is intuitively reducible to an expreflion 
fo much more fimple. Mr. Harris in his Optics, and Doétor 
Prieftley in his Hiftory of Vifion, &c. defcribe the contrivance 
in general, as confifting in cementing together two like concavo- 
convex glafles, with water between them, the radii of whofe fur- 
faces fhall have a-certain ratio to each other; but neither of them 
tell us what that ratio fhould be. An inveftigation of the de- 
monftration of this conftruction is therefore defirable, not only 
on its own account, but alfo as it may lead to a correction of 
Newton’s text, which, from what has been obferved, appears ma- 
nifeftly to be corrupt. 
Is the ratio. of 7to R denote the ratio of the fine of incidence 
to the fine of refraction out of glafs into air, D the radius of the 
{pherical 
