Monthl , 
JOU epee. of Immersion Lenses. 135 
lenses. The nascent pencil successively encounters variable resist- 
ances, and finally, in the water lens, attains much less obliquity of 
transmission. 
And, as explained in the first part, an immersion objective of 
80° aperture gathers as large a nascent pencil from a shining par- 
Gene = VLU we ME eos ae i ae) 
= SSS | ZZ 
ESE 
———sI 
——=G 
AXIS 
Object Q being mounted dry without Balsam 
ticle Q as a dry objective of 120° aperture: the great bulk of the 
nascent rays passing more centrically through the water film.* 
T will avail myself here of some known results of the immer- 
sion system. 
Dr. Woodward could only effect the resolution and enumeration 
of Nobert’s XIXth Band by means of the Powell and Lealand 
Immersion ;;th, not by the dry lens. These opticians cannot show 
the markings of the Acus or Amphipleura pellucida except by the 
immersion lens, which, as already stated, 1s able to gather up a 
volume of oblique rays nascent from the illuminated particle vid 
water, which are impossible wid air (for a Canada-balsam mounted 
object) ; the quantity of nascent rays, and which are really the 
best defining rays, being, as compared with air refraction, as 2} to 1, 
to be shown farther on. 
Again, if the minute spherular bodies detached from diatoms 
—especially those scattered in the vicinity of Angulata—be steadily 
examined both with the dry and immersion lens of the finest qua- 
lity, the confused halo disguising the true definition of the particle 
as a luminous fog is much less apparent in the water lens. The 
* The course of each of the rays is laid down by the Deviation Tables. 
VOL. IV. L 
