ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
42.1 
on a piece of white paper l>y the side of the Microscope. With the free 
right eye he guides the pencil in tracing on the paper the magnified map 
of the object. (3) In using the camera lucida a single eye is used for 
observing the object on the slide, as well as for guiding the pencil in 
tracing its reflected image. Method 1 requires a good memory and 
considerable skill as a draughtsman. No. 2, less skill is required, but 
the knack of doing it can only be obtained by practice. With No. 3, 
reasonably normal vision is a pre-requisite. The writer has for a long 
time, perhaps always, been affected with astigmatism and hypermetropia, 
to which advancing years have added presbyopia, and in consequence is 
unable to use the camera lucida with satisfaction. In No. 1, binocular 
vision is employed in the operation of drawing ; in No. 2, monocular 
vision ; and in 3, semi-ocular vision. 
The inconveniences referred to may be avoided by a simple device, 
which the writer has of late used with some satisfaction, namely, a right- 
angled prism with silvered hypothenuse. This should be mounted with 
a short tube extending from one of the square surfaces, and of suitable 
size to enter the tube of the Microscope. A similar short tube of a sizo 
to receive the ordinary eye-piece extends from the other square face of 
the prism. If now the Microscope be placed with the tube horizontal 
and the prism case with eye-piece be inserted, the ocular pointed down- 
ward, an imago of the object on the stage will be projected on a piece 
of drawing paper beneath, provided of course that there is sufficient 
illumination beyond the stage, and that no light reaches the paper except 
that coming through the objective. Personally I find this instrument 
much more convenient and satisfactory than the camera lucida. 
Mechanical micrograms must yield, however, to photographs ; and the 
micrographic science of the future will seek the aid of the pencil less, 
and make more frequent use of the convenience and accuracy of photo- 
graphy. Bausch & Tomb made and mounted for me the prism described, 
and I have no doubt will be pleased to duplicate it for others/’ 
Kikschmann, A — Ueber die Herstellung monochromatischen Lichtes. (On the 
Production of Monochromatic Light.) 
Wundt, Philos. Stud., 189(>. 
Zeitsclir. f. Wise. Mihr., VIII. (1891) p. 420. 
(4) Photomicrography. 
Text-book of Photomicrography.* — The aim of the author in this 
text-book has been to give an account of the more important contribu- 
tions to the now rapidly increasing literature of photomicrography. 
Nothing in this direction has been attempted since the appearance of 
Moitessier’s excellent work in 1866. The author traces out the historical 
development of the apparatus and methods of photomicrography, and 
shows how the processes now in use were gradually perfected. The 
book is divided into eight sections. The first treats of the apparatus 
required for photomicrography from the general point of view of its pro- 
duction and adjustment; while the second deals with optical questions, and 
gives a history of the gradual development of objectives and eye-pieces. 
In the third section the various sources of light are described, and the 
* ‘ Lehrbuch der Mikropbotographie,’ by Dr. Richard Neuhaus, Braunschweig 
See Ceutral-Ztg. f. Optik u. Merhanik, xii. (1891) p. 282. 
