454 C. A. Young—Oolor Correction of Achromatic Object Glasses. 
Art. LIX.—The Color Correction of certain Achromatic Object 
Glasses ; by Prof. C. A. Youn, Princeton, New Jersey. 
a nearly equiconvex lens of crown, and a nearly plano-concave 
int. 
The other lens is that of the Equatorial belonging to the ob- 
servatory of the John C. Green School of Science at Princeton. 
It has an aperture of 9°5 inches and a focal length of 188. It 
is constructed substantially upon the curves proposed by Gauss 
Gauss’ Werke, vol. v, p. 507, Géttingen Ed.), the radii and 
constants of the objective being as follows, viz: 
hes. 
Crown lens, meniscus, Radius of convex surface, 16°72 
convex side outward t Radius of concave surface, 57°425 
Thickness at center. 620 
Interval between lenses, 0°312 
Flint lens, concavo convex, ) Radius of convex surface, 20°684 
convex side next crown, Radi 
from ten to twenty for each line of the spectrum examined ; 
the figures for the Dartmouth instrument depend upon only 
five measurements each, and are of course somewhat less reli- 
abl 
e. 
The method of observation was in all cases substantially the 
