The belly must be composed of two parts, and has to be joined together so exactly that the narrow year-rings are in the middle of the same; the outer ring which should not be more than 2 m/m. broad and very equally disposed, may run towards the edges. The edges must be of the same thickness as those of the back.
VI. THE ARCHING.
It does not seem to me probable that Stradivarius acted without mature deliberation in making the arch of the back and belly, taken together, of the same height as the ribs, viz.: 30 m/m.; of course, I am speaking now of the violins made during his prime. If the back and belly are placed one upon the other, the height will amount to 30 m/m., the entire external diameter, therefore, must be 60 m/m., since the ribs, as already stated, have a height of 30 m/m. I am certainly of the opinion, that Stradivarius substantiated these proportions by experiments. There are, however, exceptions; the greatest of the deviations from this rule which has come under my notice, consisted in the middle line measuring 70 m/m., reckoning from the upper edge of the belly to the lower edge of the back. No doubt, this violin, made in 1710, was an experiment, the average measurement being considered to be from 58 to 62 m/m. Now and again, Stradivarius made the arch lower, whether intentionally or from want of wood, I am not in a position to say. In this case he makes the ribs correspondingly higher, so that the above-mentioned measurement may still be 60 m/m. Stradivarius has also occasionally made the arch of the back less than 15 m/m., and by way of compensation, in this case, has increased the arch of the belly. I am of opinion, however, that these deviations are to be ascribed more to experiment than to accident. He never trusted to chance in his work, but in the most careful way reflected upon it and took into consideration all circumstances in connection with it. The arch given as an example in Fig. 6, is taken from a Stradivarius violin of the year 1713, and as the belly and back are both of equal height, viz.: 15 m/m., the entire height amounts to 60 m/m.
VII. THE PURFLING.
The purfling is always placed 4 m/m. from the edge and is 1¹⁄₂ m/m. wide. It consists of three parts, the two outermost of which are prepared from maple and stained black, while the middle part is made of the same kind of wood, but unstained. It is of the utmost importance that the purfling should only be inserted to the depth of one-third of the thickness of the edges, otherwise the edge will very easily break off. In the work of Stradivarius, one finds continually on the back, both above and below, a peg of maple-wood, by means of which he fastened the back to the block, and the half of this peg is inserted in the purfling. In violins having a divided back, one finds another purfling on the bottom block, along the joint of the ribs, but with backs made in one piece it scarcely ever occurs, because then the under ribs, as far as the middle rib, are prepared in one piece. The purfling is not to be regarded as an embellishment, as many suppose it is. It considerably strengthens the back and the belly towards the edges, and at the same time offers a protection, especially for the belly, against cracks, if the instrument, for example, should be opened for repairs by an inexperienced workman. I will even go so far as to assert that if the purfling were not employed, old violins could not exist without numberless cracks, for any violent blow would cause cracks, without the additional strength given by the purfling, and the greater number of old and costly violins would come down to us spoilt, or at least damaged.
The purfling also has this advantage that if perchance the edges get broken off, they can easily be replaced and the good appearance of the instrument restored without much trouble.
VIII. WORKING-OUT THE THICKNESSES OF THE BELLY AND BACK.
The thickness of the breast in the back amounts to 4 m/m. at the spot where the sound-post stands and remains the same to a distance of 50 m/m. towards the bottom block, and 60 m/m. towards the upper block, while it decreases to 3 m/m. towards the middle rib. The cheeks must be 1 to 2 m/m. thick. I have assured myself by numberless measurements that Stradivarius often changed the thickness of the back; and has even gone so far as to make it 6 m/m., while the belly which he made from the soundest and most perfect wood, with very evenly disposed grain, measured always exactly 2¹⁄₂ m/m.
IX. THE F-HOLES.
A well-formed and proportioned F has a great deal to do with enhancing the appearance of a violin. The F represented in Fig. 7 is a most perfect specimen of what it should be. Anyone wishing to cut the F-holes in the belly, should take Fig. 7 and place it in such a way that the line a/a be exactly 195 m/m. from the outer and upper edge, and b b almost upon the point of the belly. This will give the right position of the F-holes and at the same time the measurement of the body. The greatest width of the opening of the F-holes must be 6 m/m. The width of the breast between the two upper excisions must never be narrower than the width of the bridge. In the accompanying illustration these are very wide apart and might without disadvantage be placed 2 m/m. nearer together. On violins where this distance of the F-holes is less than 40 m/m., either a narrower bridge must be used or the bass-bar must be cut out a little, so that the latter may lie close on to the upper F-hole. The lower lobes of the F-holes are always slanted outwards by Stradivarius, thus presenting a more symmetrical appearance. Both incisions are small, but clearly cut.