ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
783 
improvement on that of Dr. Giesenhagen, described in this Journal, 
1891, p. 291. The latter instrument, as seen in figs. 80 and 31 (loc. cit.), 
was lacking in stability. In the design of the present apparatus the 
author was guided by the following principles : — 
(1) Microscope and drawing-table must be rigidly connected together 
upon the same base-plate. (2) The plane of the drawing must be at 
the normal distance of distinct vision, i. e. 250 mm. from the eye of the 
observer, since (3) in general the drawing should correspond in its 
dimensions with the microscopic magnification, and therefore also 
(4) the drawing-desk must be adjustable in height and in inclination to 
the Microscope. 
The mode of construction of the desk is seen in fig. 109. 
On a base-plate, 25 x 44 cm., supported on three short feet, at dis- 
tances from its left edge of 11*5 and 28*5 cm. respectively, are hinged 
two frames, each 15 cm. high, which are connected above with an 
upper plate, 25 by 38 cm. The frame on the left is directly hinged to this 
upper plate, while the other is only connected with it by means of a 
sliding-piece which is adjustable by a screw. By means of the arc-guide 
and clamping screw on the first frame the upper plate can be raised and 
fixed in any position, while its inclination can be regulated by drawing 
out the slide in the second. A sector of 10° on the upper plate gives 
its inclination. The height above the base-plate to which it can be 
raised is from 3 cm. to 17 cm. 
The drawing-board proper moves in a swallow-tail groove on the 
upper plate and is clamped by a binding-screw. The Microscope is 
screwed on the free portion of the base-plate to the left of the first frame. 
Improved Means of Obtaining Critical Illumination for the 
Microscope : Piffard’s Electric Lamp.* — Dr. H. G. Piffard being unable 
to use with comfort either gas or an oil lamp in microscopic work, and 
finding that he could work by electric light for several hours continu- 
ously without inconvenience, applied to the Edison Lamp Works for a 
lamp to be constructed according to his own specifications. These were 
carried out, and the result was a lamp of fifteen candle-power requiring 
a current of about 3 amperes under a pressure of 15 volts. The lamp 
(fig. 110) has a cylindrical glass bulb about 3 in. long by 1 in. wide. 
The carbon filament is much broader and thicker than in the ordinary 
electric lamp, and is only 3/4 in. long, while the rest of the apparent 
filament is composed of copper wire arranged so as to support the carbon 
in a vertical position. When the carbon is rendered incandescent it 
shows a streak of light of intense brilliancy about 3/4 in. long and 
apparently 1/8 in. wide. The minified image of this is focused bv 
mirror or condenser on the object and constitutes “ critical ” illumina- 
tion. On examining the object with a 1/4 in. objective it was found that 
the field was not evenly illuminated, as there was a central brilliant 
streak on each side of which the light was comparatively feeble ; but the 
portion of the object within the area of the streak was illuminated in the 
manner most favourable for the revelation of its intimate structure. In 
systematic work critical illumination is rarely called for except as a 
* New York Med. Journ., lvi. (1892) pp. 71-2. 
