discrimination has to be exercised in selecting the hair as
in the case with the wood, for it is essential that every hair in the
bow be absolutely cylindrical and of equal thickness throughout.
These have to be sought for very carefully and are not so plentiful
as one would suppose, for the shape of a hair is regulated by that of
the pore from which it grows and these are seldom circular, many
being flat on one side, some, even, square or triangular. It has been
estimated that the proportion of suitable hairs is not more than ten
per cent. Tourte, according to Fetis, always preferred French hair
for his bows as he found it "larger and stronger than that of other
countries." I believe at present a quantity of Russian hair is used.

Tourte's daughter was of great assistance to him in selecting and
preparing the hair. His method was to thoroughly cleanse the hair
with ordinary soap, then to soak it in bran water and then, after
removing all foreign matter, to dip in "blue water." A few years ago
some misguided people tried bleaching the hair chemically. This,
however, made it quite dry and brittle, and it has happily been
abandoned.

The average number of hairs in a bow now-a-days is from 150 to 200.
In Tourte's day a similar number were used.

A few words on the structure and action of bow hair and the real part
played by rosin may not be amiss. As Mr. Heron-Allen truly observes
"it is astonishing how few violinists know anything about the
mechanical and scientific action of powdered rosin on tone
production." And for the laity he says again that many think, when
they see a bow being rosined, that it is being "greased to make it go
faster."

If we examine a hair microscopically we discover a surface covered
with minute scales. Ordinarily these scales lie close to the main
shaft, but when rosin is rubbed along the hair small particles get
fixed under the scales causing them to stand up somewhat like the
teeth of a saw. These erected scales act on the string like so many
infinitesimal _plectra_ and thus produce in perfection the sustained
sound attempted in a grosser manner by the tremolo of the mandoline.
It is simply a rapid series of shocks. A moment's consideration will
suffice to realize that continuous pressure on a string would act as
a deterrent rather than a promoter of vibration. In fact an unrosined
bow gives continuous pressure and therefore produces no sound.

The hair is usually inserted in a bow in th