carried out with extreme care right up to the head.
The next operation is to lay the pattern (Fig. 35) on the projecting
block and, with a fine pointed pencil, to mark out the outline of the
head. This is the only part of the work on the stick itself wherein
the eye is assisted by actual measurement or pattern. The shaping, or
modelling of the head, as also, later, the gradation in thickness of
the stick depending entirely upon optic precision. The absolute
accuracy of hand and eye required for such work is only to be
attained by long years of constant application.

[Illustration: FIG. 34.]

[Illustration: FIG. 35.]

After roughly shaping the head comes the delicate operation of
"setting." This is also known as putting in the "spring" or _cambre_.
The principle upon which the amount of curve is determined is that an
imaginary straight line drawn from the face of the head to the face
of the nut shall coincide with the stick at the point of its greatest
deviation from the horizontal. There is no fixed distance from either
end for this extreme point of deviation to occur. It is a matter that
rests entirely on the judgment of the maker, who, if thoroughly
experienced, regulates the curve by any variation in rigidity he may
discover in the stick. Thus should his observations point to the fact
that a certain portion of the stick is slightly weaker than the rest,
there will he put the greatest amount of "spring." It must be
understood, however, that a good maker never uses a stick that is
palpably unequal. He will only take this trouble to correct
infinitesimal weaknesses (discernible only to a hand of great
experience) in wood of exceptionally good grain. It is astonishing
how many violinists seem to think good bows are made by accident. Few
know that there are some men who can _make_ a fine bow.

The prime factor in the "setting" of a bow is heat, by the judicious
application of which the straight rod is made to assume and retain
the desired _cambre_. The heat used now-a-days is that produced by an
ordinary gas flame. Dry heat is absolutely essential, as the
slightest moisture draws all the pigmentary matter out of the cells
in the wood and leaves the bow as colourless and mean in appearance
as a stick of deal. As it is, with dry heat even, the amount of
colour exuded by a good stick during this process is quite enough to
stain the hands a deep purple.

The great point to be observed in "setting" a bow is to make sure