ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
385 
The annexed diagram (fig. 36) illustrates the division of pencils 
proceeding from the first image formed in the apparatus, and their 
general course to emergence at the two eye- surfaces. When the eye- 
piece is constructed of the form as here shown, the field is produced 
very satisfactorily, and of tolerable expansion ; and does not necessitate 
more than 4*5 inches extension beyond the Microscope-body. The 
draw-tube can be as well withdrawn, and the eye-piece occupy its place, 
thus diminishing somewhat the total extent of the instrument. With 
proper modifications of the system of lenses placed before the prisms in 
the eye-piece, the whole binocular arrangement can be brought still 
nearer the objective, and retain also all the characteristics of the 
binocular eye-piece as contradistinguished from the binocular Micro- 
scope known and in use. 
The objection that loss of light must occur on account of the addi- 
tional front system of lenses pertaining to an erecting eye-piece (the 
lower system in the diagram), of course militates against the arrange- 
ment ; but there are, on the other hand, incidental advantages in the use 
of the erecting form As the object is for the sake of efficiency 
with a high-power objective, to give as large an area to the transmitted 
pencil as possible at the point where it undergoes division in the small 
prism, therefore the power of the front system should be kept down, and 
amplification, as far as necessary in the eye-piece, be produced after the 
division has taken place 
1890. . 2 E 
