THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOUR 



Washington, D. C, December, 1884. 



YoL. Y. 



No. 12. 



Schroder's Camera Lucida. 



Although mention has several times 

 been made of this instrument in 

 these pages, we have not yet de- 

 scribed the precise construction of 

 the prism. It is figured in the cut 

 (Fig. 29), which shows the course 

 of the rays of light and the angle 

 at which they enter the prism from 

 the paper. 



The eye is supposed to be lo- 

 cated at K, immediately above the 

 prism, looking directly downward 

 at the drawing-paper and pencil, i 

 in the direction k j, the sides d e -*-" 

 and B c being parallel. The pen- 

 cil point is, therefore, seen as 

 clearly as it would be through a 

 plain piece of glass. 



The image from the microscope 

 is received on the face f c, the 

 stand being inclined at an angle of 45°. 

 The rays, being totally reflected from 

 the surface e f, are received on the 

 face D G of the upper prism, which 

 is separated from the lower prism 

 by a thin film of air. From thence 

 the rays pass to the eye, and the im- 

 ages of pencil, paper and object on 

 the stage are received by the eye to- 

 gether. 



When the light is properly adjusted 

 this instrument leaves nothing to be 

 desired ; pencil, drawing and object 

 are distinctly seen, and the light is 

 easily managed. This instrument 

 is manufactured by Messrs. Ross & 

 Co., of London, and Mr. Walmsley 

 some time ago told us he would soon 

 have some of them in stock. The 

 prism, as some readers will recog- 

 nize, is the same as was first applied 

 by Mr. Wenham as a binocular prism 



for microscopes. Not many of those 

 pi'isms were made for that purpose, 

 however, probably owing to the diffi- 

 culties of construction. 



While commending this instrument 

 in the highest terms, it is but fair to 

 say that, owing to the considerable 



Fig. 29. — Schroder's Camera Lucida. 



distance the light has to travel through 

 it from the eye-lens, it can only be 

 used with oculars of low power, hav. 

 ing a long focus back of the eye-lens- 

 Otherwise the rays come to a focus 

 within the prism, or at least do not 

 reach the point k far enough above 

 the prism to afford a sufficiently large 

 field of view. This fact will greatly 

 restrict the use of this otherwise most 

 excellent camera lucida 



No such objection applies to the 

 camera lucida of Grunow, which is 

 the only one comparable with it. In 

 fact, after showing the Schroder in- 

 strument to a well-known mici"oscop- 

 ist who v^as constantly using Gru- 

 now's form, he was quite unwilling 

 to admit that either form was superior 

 to the other as regards the clearness 

 with which the image and pencil can 

 be seen together. 



