1886. | Microscopy. 1071 
little more than to fill out the closing lines, and would have made 
the paper little longer. It will probably be a long time before any 
other author half so qualified as Dr. Brinton will try to cover the 
whole ground of American archeology. 
MICROSCOPY.! 
Revotvinc Automatic Microtome.—The microtome repre- 
= sented in the accompanying cut is the invention of Adam Pfeifer, 
mechanic and instrument-maker to the Biological Laboratory of 
the Johns Hopkins University. 
e machine is designed to save time and labor in the prepa- 
ration of series of sections, and to attain at the same time the 
_ greatest uniformity in the thickness of the sections. 
The mechanism is very simple. The frame (Fig. B) contains 
a horizontal screw beneath the sliding carriage (C). car- 
riage carries the knife (X). This carriage is moved forward by 
turning of screw. Two arms of the frame support the axis tj} 
of the revolving wheel (Æ), to which the imbedded object is 
attached. The knife (Æ) is clamped in an upright position on 
the arms rising from the sliding carriage, so that the edge of the 
-knife is in the same horizontal plane with the center of the axis 
(/). Thus, as the sliding carriage is moved by the screw, so the 
knife is moved to or from the revolving object. The carriage 
slides by means of grooves on raised tracks of the frame, and is 
not directly connected with the screw, but is simply pushed by 
nut (X). This arrangement makes it impossible that any slight 
eccentricity of the screw should cause a jolting of the carriage. 
The head of the screw is a solid wheel (M) at the end of the 
frame, and has 250 ratchet-teeth on its circumference. The screw 
has twenty threads to the inch (=.025™). The knife, therefore, 
is moved an inch by twenty revolutions of the screw; and as 
there are 250 teeth to the revolution, each tooth represents 
__*__ = _*_ inch (.005™"). : 
20 X 250 000 
The handle (O) turns the axis (/), to which is attached the 
wheel (Æ). This wheel is four inches in diameter, and to it is 
fastened the clamp which holds the object to be cut. The axis 
also carries a fly-wheel and an adjustable eccentric wheel (W), 
which is figured apart in a corner of the illustration. This eccen- 
tric moves a lever (Z), the long arm of which is connected with 
the small chain (D). The chain lifts a small lever (F), which 
works by means of a catch (Z) on the teeth of the screw-head, 
causing the screw to revolve. The small lever is steadied and 
pulled back to its place by a spiral spring (P), while another 
spring-catch underneath the frame prevents the ratchet-wheel 
from turning back. By properly adjusting the eccentric wheel | 
7 a Edited by Dr. C. O, WHITMAN, Mus. Comparative Zodlogy, Cambridge, Mass. 
