( <? 1 ! ) 
E X p E r i M E N T IV. Fig. VIII. 
Tf. ma ^ e more evidenf, and compare together the 
facilities with which Light paffes through the two 
cdiums, I took a Cube of Glafs of three Inches the 
bide, A a b B d DC, whole Seftion is A B C D and 
poking upon it from E to fee by Refledion the Candle 
jp 5 * tW ° * ma 3 es °f 11 5 one at ^ very faint, and re- 
Hefted from the upper Surface A B, and the other at * 
very flrong, and reflected from the lower Surface C D 
Now it is evident, that theVividnefs (or Brightnefs) 
of the Image *, is to theVividnefs of the Image k ; as the 
facility with which the Rays, in thefe Circumftances 
pafs through the Glafs, or through the Air: and thofe 
are eafily compared, becaufe both the Images are feen 
at once. 
Experiment V. F i g. IX. 
The Line P I being perpendicular to the reflecting 
Plane A B of the Triangle ACB, I brought the Can- 
die K by Degrees fo near to P, as to diminilh very much 
the Angle of Incidence K.I P, which made the Image or 
Appearance of the Candle at k , become fainter by 
Degrees, and at laft as faint as in Fig. 6. 
E X P E R I M E N T VI. F i G. X. 
Having made the Experiment as at Fig . 7 , I prefled 
another Prifm DFG, clofe to the Prifm A*BC, and 
when I fqueezed them together but gently, fome of 
M m m m z t h e 
