[ l 9° ] 
VI. 
But to explain this matter a little farther, and ob- 
viate fome difficulties concerning it, I ffiall add the 
following 
EXAMPLES. 
The refraCtive powers being as marked above, let 
red rays fall from glafs into air at the angle of inci- 
dence 20°, the angle of refraction will be 31° 47'. 
Again, let them fall from water into air at an 
angle of 34 0 1 ', making their angle of refraction 
48° 5'. 
And the difference of the fines of 31 0 47', and 20° 
will be precifely equal to the difference of the lines 
of 48° 5', and 34 0 1 '. 
At the fame angles of incidence 20° and 34° L, 
let the violet rays fall from glafs and water into air ; 
and the angle of refraCtion from the glafs, will be 
32° 14T. nearly, and that from the water will be 48° 
38' nearly, And the difference of the fines of 3 2° 
14C1 and 20 0 will equal the difference of the fines of 
48° 38' and 34 0 i', within .000488, or lefs than 
~o-W h part. 
We fee like wife that the red and violet rays diverg- 
ed from the glafs medium at an angle of 27'J-; but 
from the water at an angle of 33' j making the diffe- 
rence of divergence in this example 5T; that is .1 
of the whole divergence of the red and violet rays 
when retraCted from glafs into air, at incid. 20°. 
Whence 
