It is quite a reasonable supposition that most, if not all, of the personal pupils were taught by the master, or had the way pointed out to them by which they might, with the right ear for discrimination of tone quality and enough of industry, impart to their works the identical qualities of those of their teacher. But what are the facts left for our consideration in connection with caliper measurement? the pupils admittedly of his teaching, among whom we may mention Lorenzo Guadagnini, his son Joannes Battista, Alexandri Gagliano, one or two of his sons and Carlo Bergonzi, as the best known, each adopted their own, or shall we say, left no more evidence for us of having a set rule for thicknesses than their master. The nearest approach to the asserted system of Stradivari, that of a gentle declination of substance in the wood down to the edge, was made by Lorenzo Guadagnini in his extra sized violins; but then the tone, wonderfully fine, is not Stradivari, but Guadagnini. Carlo Bergonzi's system, if we may for a moment call it, was quite unlike Stradivari, and yet connoisseurs have frequently credited him with having got "the same beautiful quality of tone." From these few references it will be sufficiently plain that the grand secret of tone quality must not be sought for with the aid of calipers, so we will dismiss this part of our subject and proceed to other considerations. Besides those who have pinned their faith to the thicknesses, there are those who take up with the "air mass" theory. I am afraid the arguments in favour of this last will not bear even so much knocking about as those just considered.