192 
IOWA ACADEMY OF SCIENCES. 
one-half inch less in diameter than the glass disk. The 
cone should have an altitude of about six inches. The 
altitude depends somewhat upon the size of the scales 
used. The cone must be accurately turned and the base 
must be trued up while the piece is still in the lathe. 
Fasten the glass disk to the base of the cone by means of 
any good laboratory wax. I have found it to be the most 
satisfactory to use a wax that will melt at a low degree 
of heat. The glass can be heated to a degree sufficient to 
melt the wax over an asbestos pad placed upon a ring 
stand above a flame. As the wax melts flow it around 
evenly on the upper side of the disk, and set the base of 
the cone in it. To center the cone upon the disk previous 
to melting the wax a circle (a) fig. 2, the exact diameter 
of the glass disk should have been marked on a piece of 
paper. Using the same center (c) mark out another circle 
(b) having the same diameter as the base of the cone. 
Slip the paper under the glass disk on the asbestos pad, 
and place^it so that the circumference just coincides with 
the circle (b). If the wax is not too thick and opaque the 
inner circle can be seen through the glass, and serves to 
locate the base of the cone so that it is equally distant 
from the circumference of the glass disk. A small hook 
can be accurately screwed into the apex of the cone for 
suspending it to the scale beam. 
The glass disk should be made of plate glass not less 
than one-fourth inch in thickness, and if it is one-half inch 
it is all the better. The disk can be made by first cutting 
out a plate as nearly round as possible with a good glass 
cutter. Corners of glass can be broken off after cutting 
with the glass cutter by clamping between pieces of hard 
wood in a vice, and suddenly pushing the free part of the 
