54 
a pulley, C, and back around another drum, B, mounted on the same 
axis as A. From the drum Bit is wound on areel. The drum B is 
larger than A, so that the former winds on the thread somewhat faster 
than it is paid off by the latter. In thus stretching the thread we 
apply a force to the pulley C tending to draw it from its normal posi- 
tion. This pulley is attached to the base of a pendulum, D, which, 
under the action of the force mentioned, is drawn from the perpendicu- 
lar. The weight of this pendulum overcoming this applied force to an 
extent inversely proportional to the mean section of the Jength of thread 
submitted to the test, the position of equilibrium taken by the pendu- 
lum depends upon that mean section. This length of thread is the 
piece between the two drums A and B, and as, through the constant 
action of the machine, successive lengths of thread occupy the position 
indicated, the pendulum oscillates through a course which depends upon 
the irregularities of the thread. These irregularities are graphically re- 
corded by a pencil, H, attached to the pendulum, upon a band of paper, 
F, constantly moving under its point. In the commercial form of the 
machine the mechanism for driving the reel is so constructed as to stop 
automatically when a standard échevette has been wound upon it, and 
this échevette may then be sized in the manner above described. 
The elasticity and the tenacity of raw silk are determined by the use 
of the serimeter. This machine is composed of a dynamometer above, 
a graduated circle indicating the tension corresponding to the point at 
which the index stops. On the lower extremity of this dynamometer is 
a knob to which the thread to be tested may be attached. At 50 cen- 
timeters below this knob, in the same vertical line, is another knob 
attached to a counterweight which is on the inside of the case of the 
instrument and which also bears a pointer moving along a graduated 
scale on the outside of the case. This weight is held in place by a 
detent which is terminated on the outside of the case by a faller, on 
which it is only necessary to press lightly to cause the detent to let go 
the counterweight and permit its index to slide along the scale; these 
stop instantly, on the other hand, when the faller is released and retakes 
its initial position. 
The silk thread attached to the two knobs mentioned passes over this 
faller, and, as it tends to pull it from its normal position, the detent 
lets go the counterweight and the thread stretches until rupture takes 
place, when the descent of the counterweight is automatically stopped. 
It is then-only necessary to read the indication of the dynamometer to 
ascertain the weight which caused the rupture. By doubling the dis- 
tance passed over by the sliding index, we have the stretch per meter 
or per cent. of elasticity. 
The elasticity or ductility of silk is about 15 to 20 per cent., being 
nearly four times superior to that of cotton. It is about the same as 
brass and slightly greater than iron; hair has only half the ductility of 
silk. 
