of Natural Philosophy. patel 14f 
no distinct image of an object could be seen bye light thus 
reflected. 
Prop. 17. Exp. The effects of a te dense medium, 2 
bounded bya convex surface, on parallel, diverging, and con-- 
verging- rays, can never be illustrated by a convex lens,” 
which produces. two successive refractions,—one by a con- 
vex surface of the denser, and the other by a concave sur- 
face of the rarer medium... The lens presents the combined — 
result of the former part of prop. 17,-aud the latter part of 
prop. 18. In particular, a conver: lend can never render . 
converging rays “less CORDETEIRES as is abeariest in a ae 
fourth Piste ea the ation Fe cps , 
cisely as oe eee Baste RK 
cs % >) es a ee Se pees Sess Sera 
a 2 \ 
of prop. 18.—Both these « s, if introduced 
at oan should “ee been placed after ee and the ce 
ner in which each illustrates both propositions should hare ‘ 
been pointed out.* 
Prop. 22. Cor. 2. . The corollary i is right; but the inves- 
tigation which is given of it, is incor rigibly wrong. By 
comparison with the sone i a be seen that it gives the 
poyiian panne the prin ae a cone aphore Moe the 
ser medium by prop. 22; and then to find by prop. pytessel 
focus of rays converging (to the point just. fooedl,): wien © 
passing out of a seen darscshncepee into a apes teouale a con- 
cave surface of the. 
rop. 26...“ The ima image aa not os distnes, cubed: the th 
plane surface on which it is received be placed at tl bondi 
mabe of the. sc at focus of the lens.” me oe she - 
“ Though the distance of the. ail ject es 
lens — , the image may be preserved distinct.w hout 
varying | the distance of the pee surface mi | receives it.” 
Th m what? ‘The seco 
eta ithe ays proceed after 
as from the inaccurate manper in which some of 
