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 the natural position of its growth, i.e., the root end at the top, thus, as the scales point downwards, giving the greatest attack to the down bow. Some have tried placing half one way and half the other but I do not think a very perceptible difference results from this proceeding.
CHAPTER X.
QUALITIES ESSENTIAL IN A BOW MAKER—SHAPING THE STICK—SETTING THE Cambre—THE FACES—THE TRENCHES—THE NUT.
The manufacture of the bow is an industry calling for rare qualities of patience and concentration on the part of its followers. The skill required is of quite a distinct kind. Strength and delicacy of hand must both be exceptionally pronounced, and mathematical accuracy of eye is essential. Delicacy of touch to readily appreciate the varying degrees of elasticity found not only in different sticks but often in the same piece of wood. Strength to work with precision in such hard wood. And for this kind of work the strength required is not that of the carpenter who can use the weight and swing of his body; it is, rather, a self-contained strength in which opposing forces must co-operate in order to ensure the absolute accuracy so indispensable in a bow. Then the sight must be of unerring judgment, for nearly all the work depends on the eye. Bow making is distinctly nervous work for it keeps the mind constantly alert.
I am indebted for most of the details given in this chapter to the late Alfred Tubbs, son of James, and a good workman, who died comparatively young in 1909. He told me that he only made one bow at a time for the reason that each stick has its own individuality, some intrinsic feature that has to be borne in mind through all the details of fitting, mounting and adjusting. The mind is apt to lose its certainty of retention when exercised on as few, even, as three sticks simultaneously. Therefore each bow is completed before the next is commenced.
Taking the rough stick as shown in Fig. 34, the first operation is that of "rounding the throat," in other words the square rod is made round for a few inches just below the rough block left for the head to be cut from, this portion being called by some the "throat," and by others the "neck" of the bow. After this the corners of the remaining square portion are planed away, thereby making the stick octagonal in section. Should it be intended that the finished bow be octagonal, naturally the throat is not rounded but the planing away of the corners is 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.