ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
101 
safety possesses some advantages over those in ordinary use. The auto- 
matic arrangement for cutting off the gas when the flame, by accident or 
otherwise, has been extinguished is novel and ingenious. Fig. 10 shows 
a single burner as used for small thermostat, and fig. 
11 a double burner for heating ordinary cultivating 
ovens. To light the burner, a match is applied for some 
seconds to the lower part of the loop at A (fig. 12). 
The vapour tension, resulting from the heating of 
the bent tube, acts upon a metal membrane which 
opens the gas valve, and keeps it open as long as the 
flame is burning. Should, however, the flame by any 
accident be extinguished, the temperature of the tube 
falls, the hydraulic pressure is diminished and the gas- 
valve is again closed. 
An Improved Form of Dr. Edinger’s Apparatus * 
for Drawing Objects under Low Powers. — Mr. E. M. 
Nelson writes to us : — “ The following is a description 
of the instrument made and exhibited for me by Mr. 
Curties, at the special exhibition on November 30th. 
My improvement consists in securing a far larger 
angle from the source of illumination and then condensing it so that it 
may all pass through the front lens of the objective, which on that occa- 
sion was a Zeiss aa. This increased illumination will, I think, be found 
to be an improvement on Dr. Edinger’s method. 
On referring to fig. 13 it will be seen that the magnified image 
of the object is projected on the paper so that there is no troublesome 
camera or other apparatus to look through, and no previous knowledge 
or practice in drawing is necessary. 
The outline of the image is directly traced on the paper on which it 
is projected, in the same way that a magic lantern view might be traced 
on the sheet on which it was cast. 
The instrument consists of a vertical board A B, with a tube C 
fitted at right angles to it ; this tube has a mirror M of common looking- 
glass fixed at an angle of 45°. Below this there is a specially con- 
structed condenser D E, consisting of two lenses D and E such that 
either of them can be used independently or they may be used together 
as in the figure. For very low powers the large lens D is alone used, 
for higher powers the small one E, while for still higher both D and E 
are used together. T is a simple stage, the slide being held against the 
lower side of it by spring clips. On the upper side there is a wheel of 
diaphragms ; the use of this wheel of diaphragms is totally distinct from 
that in an ordinary Microscope, where its office is to regulate the angle 
of the cone of illumination, because here it merely limits the size of the 
field. O is the objective (for a medium power a Zeiss a a will be found 
very suitable). Both the objective-holder O and the stage F are fixed 
to a separate block GH which slides in grooves on the board AB, and 
is clamped by the screw S. 
This arrangement allows the stage and the objective to be placed at 
a proper distance from the condenser. The illumination of an object in 
projection, especially in low power projection, differs essentially from 
* See this Journal, 1891, p. 812. 
Fia. 12. 
