ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
233 
Now as most unmounted objects are seen by reflected light, for it is 
only prepared objects that are suitable for examination by transmitted 
light, a lens of this kind is of great service in the field. An object 
examined by this lens when held up towards a bright part of the sky is 
strongly illuminated and looks altogether a different thing. For dissect- 
ing purposes it is a convenient combined lens and illuminator, and is 
much easier to manage than other methods now in vogue, such for 
example as that of Mr. Cheshire which was exhibited here some years 
ago* 
The lace-work on the egg of a house-fly can be seen. The object 
under it this evening is the egg of the parasite of the Ground Hornbill.” 
Sources of Light for the Projection Lamp.f — Herr J. Lutzen de- 
scribes some of the latest projection instruments made in Germany, and 
gives an account of the various methods of illumination which have 
been made use of in such instruments. In fig. 36 is shown the 10J cm. 
scioptikon for school work made by Meckel in Berlin. This apparatus 
is made of the best steel and contains no soldering. 
The different methods of illumination can be divided into three 
groups. Electricity in the form of the arc-light is the most perfect, but 
on many grounds can seldom be used. Then we have the illumination 
with oxygen, and lastly without the use of oxygen. Of these two kinds 
the burners in which a stream of oxygen is used give a light which is 
nearest to the electric. Illumination without a stream of oxygen, as 
Fig. 36. 
petroleum light, Auer’s incandescent light, or magnesium light, is not to 
be recommended. The petroleum light is not bright and has a yellow 
colour ; the gas incandescent light does not give sharply defined images, 
and is not very intense ; while the magnesium light burns unsteadily 
and forms a deposit on the lenses. If these disadvantages, however, 
could be obviated, this last light would be preferable to any other. 
The introduction of the oxygen-burner has had a revolutionary 
influence in methods of projection. A peculiarity of these burners is 
that they produce a source of light approximating to the point form, 
and give a clear quiet white light. When properly constructed they are 
* Carpenter on the Microscope, 9tli edition, p. 344,' fig. 289. 
f Central.-Ztg. f. Optik u. Mechanik, xvi. (1895) pp. 14-6. 
