me that annealing
of the threads can be avoided. On the other hand, it may be possible
that a thread cooled slowly from the first does not suffer in the same
way as a cold thread would do when annealed in a Bunsen flame.

Again the velocity of the gases is beyond doubt exceedingly high, so
that the annealing, even supposing it to be deleterious, might not be
carried very far. Threads drawn by this method and measured "dry,"
i.e. by mounting them on a slide without the addition of any liquid,
turned out to have a diameter of about 1/20000 of an inch.

I do not think I could manage to mount such fine threads without very
special trouble. All the threads lying on the board, however, were
found in reality to consist of three or four separate threads, and
there is no reason why several threads should not be mounted in
parallel, provided, of course, that they are equally stretched and
touching each other. Equality of tension in the mounting could be
secured by making one attachment good, then cementing the other
attachment to the other end of the threads, and "drawing" the two
attachments slightly apart at the moment the cement commences to set.
This method may turn out to be very valuable, for, so far as I can
see, the carrying power would be increased without an increase of
torsional stiffness of anything like so high an order as would be the
case were one thread only employed. On the other hand, the law of
torsion could hardly be quite so simple, at all events, to the second
order of approximations.

Sec. 88. Properties of Threads.

A large number of experiments on the numerical values of the elastic
constants of quartz threads have been made by Mr. Boys and his
students, and by the writer. As the methods employed were quite
distinct and the results wholly independent, and yet in good agreement
with each other, a rounded average may be accepted with considerable
confidence.

TENACITY OF QUARTZ FIBRES (BOYS).

Diameter of Thread.

Tenacity in Tons' Weight per Square Inch of Section.

Tenacity in Dynes per Square Centimetre.

Inches

Centimetres

0.00069

0.00175

51.7

8 X 109

0.00019

0.00048

74.5

11.5 X 109

Rounded mean of Boys' and Threlfall's results:

Young's Modulus at 20 deg. C,

5.6 X 1011 C.G.S.

Modulus of Simple Rigidity at 20 deg. C,

2.65 X 1011 C.G.S.

Modulus of Incompressibility,

1.4 X 1011 C.G.S.

Modulus of Torsion,

3.7 X 1011 C.G.S.

Approxi