compound lenses and object-glasses. 
2 67 
dr dr dR dR 
Table 12. Values of — , I, — 2 
dfA 1 dp' dg dy.' 
ZJZZ 
*4_ 
dR 
1 
1 
m- 
04 
13 
dyd ~ 
djA 
rfM “ 
d, y ! 
0-50 
°-55 
coo 
-fo-o8o 
+ 0-020 
— 0-080 
2-000 
—2-520 
—2-947 
0-360 
— 0-107 
+ 0-373 
+ 30-620 
+ SO -333 
+ 53 - 16 
0-65 
0*70 
—0-273 
—0-667 
— 4" 1 ' 3 
— 5 ‘ 5 °° 
+ 1-180 
+ 3 - 1.53 
+ 69-900 
+ 75 - 7 oo 
075 
— 1-120 
“ — 7" 2 5 3 
+ 5-680 
+ 72-083 
It will be seen by this statement, that the variations of the 
curvatures arising from a variation in the refractive power of 
the flint lens, are much smaller than those produced by an 
alteration in that of the crown, which is another fortunate 
circumstance, the crown and plate glass usually met with 
being much more uniform in this respect than the flint. 
JOHN F. W. HERSCHEL. 
Slough , Feb. 19, 1821. 
MDCCCXXI. 
M m 
