PHOTOGRAPHY TO THE MICROSCOPE. 269 



Photographs of opaque objects were obtained by concen- 

 trating sunlight on the object, either with the concave mirror, 

 properly mounted, or with the plane mirror and bull's-eye 

 condenser. The \\-, 1-, and -^^-inch objectives were employed. 

 The colour of microscopic injections for this purpose should 

 be blue or white, though, Avitli a long exposure, photographs 

 were obtained of yellow injections. 



I am indebted to Dr. Wolcott Gibbs and G. T. Strong, Esq., 

 for valuable suggestions relating to the subject of this article. 



As some interest has lately been manifested with regard to 

 eye-pieces, it may be proper to state that, in the course of this 

 investigation, three eye-pieces were constructed — No. 1 on 

 the general Huyghenian plan, the eye-lens being an under- 

 corrected achromatic ; ^ the distance between the eye- and 

 field-lens could be varied at pleasure, as advised by Amici. 

 As a single microscope, its power was eight diameters. The 

 general performance of this eye-piece seemed to me somewhat 

 better than that of the plain Huyghenian eye-pieces with 

 which it was compared. 



No. 2 was a Kellner eye-piece ; the distance between the 

 lenses could be varied ; alone, it enlarged twelve diameters. 

 The performance was good. No. 3 consisted of tv/o mider- 

 corrected achromatic lenses combined, in the Huyghenian 

 manner; alone, it magnified twenty-five diameters. When 

 used as the eye-piece of a telescope, it gave a pretty good 

 image ; as a microscopic eye-piece, it was inferior to No. 2, 

 in spite of its superior magnifying power, except, perhaps, 

 when used with well-corrected objectives of large, angular 

 aperture. With all three eye-pieces the correction of the 

 objectives remained unaltered in kind.f 



Troy, New York; 

 July 1st, 1861. 



* The ortlioscopic eye-piece of Grunow consists of an eye lens partially 

 achromalized in combination witli a field lens differing iu form from tlie 

 ordinary Huyghenian. — O. N. E,. 



■f After this article \Tas in print, I received from a friend a paper of 

 Amasa M. Eaton, Esq. ' Proceedinos B. S. N. H.,' vol. viii, p. 105. 

 Mr. Eaton has devoted himself with success to the pvoduction of ambrolypes 

 of microscopic objects. — 0. N B,., Troy, N. Y., July 23rd, 1861. 



