E474] 
Add to all tliefe.Thzt a dug yfpplic^ation of Light to th: 
0^7 eff renders k Vifible, if it were not fo before ; as ap- 
pears from a dark room illuminated : or elfe makes it bet- 
ter and more truly difcerciable by the Senfe ofSMng; if be-? 
fore it might have been difcern'd. 
Hence the fame Colour in a divers Light will appear dif- 
ferent, and no TiUuvc can well be difcern'd or judg d of, 
but by it's true Zjt^/^^, Befides, the Lm«r will aflure you, 
that he can hardly make trae work or hit the Air of a face 
exadly, uolefshe draw by a North-Light, by reafon of 
the Steddinefsof that, and the uncertainty of all other 
Z/^^i^j- whatfoever. Which things fliew, that the Jrt of 
duly applying Light to th Obj^H doQS very much lielp and 
improve Vifion. So alfo does the due placing of the Ob- 
jeSl, as to Height and Dijianc . But to enumerate all things, 
that help Z)mi? Fi/ion, would be infinite. 
2. Ex parte Organi v I M dij Dired: Vifion has been im- 
proved by making ufe of zTube, without GlafTeSjOr a mans 
clos'd hand, to look' throw 5 which admitting into the 
^^^only the principal raies, that come diredly from the 
Obje l, do very much ftrengthen and clear the Sight, by 
excluding all the Collateral raies, that crouding into the 
Eye, together with the direct ones, would confound and 
difturbit, partly by mixing and interfering with the Di- 
red: raies, and partly f or rather chiefly ) by too much 
enlightening the fund of the Eye, wherein Vifion is truly 
( though then imperfedtly ) made. 
On this is founded the Art of making Spectacles without 
Glaflej"; ( as well as T^^^^/j which is done by putting into 
the Glafs-holes ( iniieed of GlaiTesj two fnortT^^^^j- of be- 
tween ? and 4 inches long f'for their length is to be vary'd 
according to the age or eye of the beholder, and fo alfo is 
the Diameter of the extream ends ) which Tz^^^J* being 
made of Spanijh Leatk r ( or paft-board, or fome fuch like 
matter ) and black'd on the infide, are fo to be plaqd, as 
that the vifual raies, receivd throw them may meet in 
one 
