ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
G27 
Tlie vertical camera represented in fig. 70 is tlie preceding camera 
(fig. 69) with the addition of a special frame for fixipg it vertically 
so that it may be used for photographing liquid preparations. 
Comparison between Petroleum, Gas, and the Auer Incandescent 
Light with respect to their Usefulness for Photomicrographic 
Work.* — Herr K. Neuhauss comes to the conclusion from his experi- 
ments that — 
(1) The Auer incandescent light is very convenient for photo- 
micrography, and the time of exposure is four times shorter with this 
light than with petroleum. 
(2) Petroleum light is to be preferred to the Argand gas-light. 
(3) No advantage for photomicrographic purposes is gained by the 
addition of camphor to petroleum. 
The disadvantage attending the use of the Auer light — that by the 
projection of the source of light in the plane of the image the luminous 
network is seen, and so no uniformly illuminated field of view 
obtained — is obviated by not exactly focusing the image of the source 
of light. No sensible diminution of the illumination is thereby pro- 
duced. 
(6) Miscellaneous. 
Plea for Systematic Instruction in the Technique of the Micro- 
scope at the University.f — Mr. Jacob D. Cox, in his presidential 
address to the American Microscopical Society, urges the desirability of 
.a somewhat extensive course of instruction in the technique of the 
Microscope in Universities. He considers that the University is the 
place where the worker should be able to find everything of value which 
has been invented in connection with the Microscope, as well as oppor- 
tunity to test its value by actual comparison in use. The exhibits of 
Microscopes and microscopical apparatus at each of the great exhibitions 
were of great value in affording scientific visitors the opportunity of 
comparing what was being done in different countries ; but of how much 
greater service would such exhibits be, if they were permanent at the 
centres of learning, open not only to inspection, but to continuous use 
under the guidance of expert teachers ! 
The author gives a brief analysis of the lines of work open to the 
microscopical student, and treats of the various points with regard to 
the technique of the Microscope which may be said to be still undecided. 
In the first place, in the case of the lenses the student needs a com- 
petent instructor to show him the differences between them, the purposes 
for which each is adapted, and the manner in which the aperture limits 
the power. In treating of immersion lenses the author insists on the 
need for collar-adjustment for cover. 
The use of the eye-pieces opens another series of problems, as to 
the distance apart of objective and ocular, the size of the field-lens, and 
the relative values of the various forms of oculars. 
The various ingenious devices which have been employed in the 
fine-adjustment, the use of the so-called sub-stage accessories, the advan- 
tages to be derived from oblique illumination and its relation to the 
* Internat. Med.-photogr. Monatschrift, i. (1894) pp. 29-30. See Eders Jahrb. 
If. Photogr. u. Keproductionstechnik, vii. (1893). 
t American Microscopical Society. Address of the President, 1893, 16 pp. 
