Instruments, it appears, should be sufficiently _well-timbered_; their durability is much affected when they are finished off too weak in wood. The bass-bar and sound-post are not inserted to strengthen the instrument (as many have supposed), but to increase the vibration. The vibratory principle, according to M. Otto, has been as yet but imperfectly investigated, and is little understood. Recent experiments, however, have somewhat further extended our knowledge of it. Great nicety is requisite as to the erection and proportions of the _bridge_: when it is too high, the effect is a dull tone, difficult to be brought out—when too low, a shrill sharp, and thin tone. In good instruments, the sound-post stands half an inch below the left foot of the bridge: in defective ones, it may be placed rather nearer, to increase the strength, and assist the tone. The screw-holes must not be rubbed with rosin to tighten them: the best appliance is chalk. Some wise-acres pretend that a violin is to be improved in tone by breaking it to pieces, and mending it again! Others disturb and shift about the bridge and sound-post, till the tone is almost gone. Others again, with a taste worthy of Hottentots, have daubed over the “belly part” with a coat of glue, mixed with powdered glass; and some there are, who have tampered with instruments by an absurd plaster of varnish and white of eggs, under the unwholesome idea of closing up the pores! It is suggested that _flies_ should not be allowed to introduce themselves into the _f_ holes. (Children say, by the by, that _f_ “_stands for fly_:” and, in the case in question, it stands _open_; so there seems, at least, a pretty good excuse for the intruders.) The inside of the instrument is to be cleaned out once in six months, by means of a handful of barley, made warm, poured in at these _f_ holes, and well shaken. The best _strings_ are those from Milan (called Roman), which are clear and transparent as glass, and should have as much recoil, when opened out, as a watchspring. A very important article of requirement is good refined rosin: the common brown rosin of commerce is quite unfit, because of its thickness and clamminess.