Marcu 14, 1884.] 
down to a pencil or stylographic pen that is 
carried on a sliding-track placed over a metal 
cylinder carrying a sheet of cross-section 
paper. It is obvious, that, as fast as the 
specimen elongates under the action of the 
stress, the pencil is drawn along the ways of 
the cylinder parallel to its axis. 
Figs. 3 and 4 show the beam and register- 
ing-cylinder. In fig. 3 it will be seen that the 
beam consists of a single bar, sustained on a 
stand at one end, and enclosed in a guard at 
the other, while on this beam there rests a 
semicircular brass box forming a poise. Along 
the top of the beam, there is cut an exceedingly 
fine rack ; and the motion of the poise is ob- 
SCIENCE. 
317 
the motion of the poise with the motion of the 
cylinder exactly, so that, in a given travel of 
the poise along the beam, the cylinder may 
move a corresponding quantity. Of course, 
the ratio between the two movements is simply 
a matter of proportioning so as to accommo- 
date the ordinary cross-section sheet to the 
circumference of the cylinder; but an exact 
and constant ratio is a very important point. 
Inside of the poise are two large wheels, about 
eight inches in diameter. The wheel placed in 
front is graduated with a series of numbers. 
The pinion carrying the poise along the beam 
is an inch in circumference, and consequently a 
single revolution of the pinion carries the poise 
Fig. 3. 
tained by a pinion placed inside of the box and 
‘gearing into thisrack. At the end of the beam 
may be seen the mercury-cups for making an 
electrical connection as the beam rises and 
falls. The operation of this piece of apparatus 
is substantially as follows. The clock-work 
motor contained in the poise, for driving it to 
and fro on the beam, is connected with the 
mercury-cups by means of some brass strips 
placed in the rear of the beam. These strips 
are connected with two electro-magnets on the 
inside of the poise: consequently, when the 
beam either rises or falls, one or the other of 
the magnets is excited, the corresponding train 
of clock-work is thrown into action, and the 
poise rolls to and fro until a balance is re- 
established. This motion of the poise to and 
fro on the beam is exceedingly simple, the 
knotty part of the problem being to correlate 
one inch along the beam. ‘The front wheel is 
secured directly to the pinion-shaft, so that 
there can be no back-lash between the two; 
and, being eight inches in diameter, one revo- 
lution of the pinion causes this dial-wheel to 
travel twenty-five inches of circumference. A 
motion of one inch along the beam corresponds 
to a weight of four thousand pounds. The dial- 
wheel being eight inches in diameter, and sub- 
divided into four hundred parts, each of these 
parts corresponds to ten thousand pounds. The 
rear wheel of the poise is constructed in pre- 
cisely the same manner as the front wheel, 
excepting that the marks on the dial are re- 
placed by little strips of India-rubber, so that 
the wheel presents a series of teeth alternately 
made of India-rubber and of brass. On this 
wheel, there presses a brass commutator-strip, 
so arranged as to include the cylinder in its 
