386 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Having obtained by this means a pencil (or beam) transmitted 
tbrongb the eye-piece of the greatest possible dimension or area, at the 
point of binocular division, greater amplification in the eye-piece, as to 
its total power, might be advantageously effected by means of lenticular 
immergent and emergent surfaces of the upper prisms ; the lower face of 
each prism to be convex, the upper emergent surfaces concave, giving achro- 
matized refraction in each case. By this means a larger field, together 
with a minimum length of tubes above the prisms, would be secured. 
By thus appropriating every surface of all the prisms not a reflecting 
surface, for the purpose of lenticular refraction, the greatest aggregate 
advantage appears to be secured.” 
We should mention that fig. 36 is not the diagram given with Mr. 
Tolies’ original paper, but is one suj)plied by him shortly before his death, 
and drawn to scale, showing the path of the rays. In sending it, he re- 
marked that without A the arrangement is a Nachet Binocular Microscope. 
Fig. 37 shows one of the earlier forms of the instrument as com- 
bined with the eye-pieces, and is reproduced from Dr. Dippel’s ‘ Hand- 
buch der Allgemeinen Mikroskopie,’ vol. ii. p. 698. Dr. Dippel points 
out that the eye-piece “ either entails a very considerable lengthening of 
the body-tube or, if this inconvenience be avoided, considerably disturbs 
Fig. 38. 
Fig. 39. 
the optical effect of most objectives, because in this case they are used 
for a far shorter imaged distance, and consequently with an essentially 
different course of rays than in ordinary use.” 
PrazmoivsHs (figs. 38 and 39) is made entirely of brass, and being 
