ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
91 
The burner is obviously an essential part of the instrument. The 
projected image only attains the maximum of sharpness and brightness 
when the light-source is formed by the condenser exactly in the centre 
of the rear primary plane of the projecting objective. 
Fig. 12 shows the burner, which is intended to secure the following 
advantages : — (1) The large lime-plate is plane, and stands perpen- 
dicularly to the optical axis of the apparatus ; (2) the whole burner 
arrangement is movable parallel to the optical axis ; (3) the nozzle- 
opening is adjustable in every direction to the optical axis, especially 
perpendicularly, by means of a micrometer-screw. The supporter of 
the burner is the massive camera back-plate w, in which the brass nuts 
f /' are inserted, carrying the brass tubes r r' , movable on the release of 
the clamp- screw a. Both are connected by the cross-bar a! c, which can 
be fixed on r' by the clamp-screw a' and on r by the screw c. By the 
screw-head d the lime-plate K in its holder can be rotated in order to 
Fig. 12. 
bring new portions of the lime into incandescence. To the tube r a 
copper ring e is screwed on, in which the micrometer-box m and at the 
same t ; me the burner-nozzle b can be moved sectorwise ; a similar 
movement, but perpendicular to the first, is imparted by c ; and a micro- 
meter-screw m allows a third very fine movement. It is therefore 
possible to bring the centre of the flame exactly in the optical axis, and 
by the pushing of r r' to bring it into the rear primary plane of the 
objective. 
The condenser consists of a concavo-convex back-lens, of 13 cm. dia- 
meter, and two plano-convex front lenses of 16 cm. diameter. By means 
of the concavo-convex lens it was possible to give to the condenser a 
high numerical aperture, and consequently attain a great light intensity. 
By the use of an objective system of 25 cm. focus and 20-fold magnifi- 
cation, the N.A. amounts to 0*G5. The condenser is also so calculated 
that the catadioptric secondary images are distributed evenly over the 
field, and completely uniform illumination is secured. 
The diapositiv e-carrier is believed by the author to be of novel design. 
