al or even of glass, if such could
be produced. The torsion of silk, though exceedingly small, is quite
sufficient to upset the working of any delicate instrument, because it
is never constant. At one time the fiber twists one way and another
time in another, and the evil effect can only be mitigated by using
large apparatus in which strong forces are developed. Any attempt that
may be made to increase the delicacy of apparatus by reducing their
dimensions is at once prevented by the relatively great importance of
the vagaries of the silk suspension.

The result, then, is this. The smallness, the length of period, and
therefore delicacy, of the instruments at the physicist's disposal
have until lately been simply limited by the behavior of silk. A more
perfect suspension means still more perfect instruments, and therefore
advance in knowledge.

It was in this way that some improvements that I was making in an
instrument for measuring radiant heat came to a deadlock about two
years ago. I would not use silk, and I could not find anything else
that would do. Spun glass, even, was far too coarse for my purpose, it
was a thousand times too stiff.

[Illustration: FIG. 5.]

There is a material invented by Wollaston long ago, which, however, I
did not try because it is so easily broken. It is platinum wire which
has been drawn in silver, and finally separated by the action of
nitric acid. A specimen about the size of a single line of silk is now
on the screen, showing the silver coating at one end (Fig. 5).

As nothing that I knew of could be obtained that would be of use to
me, I was driven to the necessity of trying by experiment to find some
new material. The result of these experiments was the development of a
process of almost ridiculous simplicity which it may be of interest
for me to show.

The apparatus consists of a small crossbow, and an arrow made of straw
with a needle point. To the tail of the arrow is attached a fine rod
of quartz which has been melted and drawn out in the oxyhydrogen jet.
I have a piece of the same material in my hand, and now after melting
their ends and joining them together, an operation which produces a
beautiful and dazzling light, all I have to do is to liberate the
string of the bow by pulling the trigger with one foot, and then if
all is well a fiber will have been drawn by the arrow, the existence
of which can be made evident by fastening to it a piece of stamp
paper.

In this