1896] BRIEFER ARTICLES 263 
used by Darwin. It consists of a diopter made out of a short metal tube 
2.5" high and 1 in diameter, having a section cut out of its lower 
half for the purpose of inserting a pen. In the inside of the tube is a 
coverslip (represented by the horizontal dotted line) with two cross 
hairs, and at the top another coverslip with a round dot upon it. Both 
the hairs and the dot are centered in the tube. When the dot at the 
top coincides with the cross hairs below, the line of vision extends 
directly through the center of the tube which rests upon the horizontal 
glass plate m. When the dot and cross hairs are made to coincide 
with the black wax point on the glass capillary attached to the plant 
(which is for the purpose of amplifying the nutation movements) a 
direct line of vision is obtained and recorded by means of a pen on 
the glass plate (m). The glass capillary is secured to the plant in the 
usual manner by means of wax, and the multiplication of the nutation 
movements can be increased or diminished by lengthening or short- 
ening it. Professor Wiesner used two horizontal glass plates instead 
of one, but since the lower part of the diopter is cut out for the pur- 
pose of inserting a pen, only one plate is necessary. -G E. STONE, 
Massachusetts A gricultural College. 
