The pneumatic principle thus applied, and the success of the attempts to adapt it to the organ, led experimenters to emulate, and if possible improve upon, the early attempts at the practical manufacture of pianoforte-playing mechanism. Without going too much into details, it may be recorded that the two concerns previously referred to were nearly ready in 1896 to come out with such an instrument, and patents were granted in 1897 for a complete piano-player of the cabinet style, attachable to any piano, and easily detachable therefrom. Other patents soon followed, and other manufacturers fell into line, with the result that the great piano-player movement had soon begun in earnest. The productions of the different firms, of course, varied in details, but only two widely separated schools have developed, and inasmuch as both of these employ the pneumatic principle, which has triumphed over all others, and is now adapted unanimously by manufacturers who desire to render possible an approximation to artistic rendition of pianoforte music, it will be unnecessary to treat of any instruments constructed on other lines.
In the meantime it will be well to note that the above short sketch of the preliminary skirmishing, as it were, is intended to be nothing more than an outline, as the policy adopted throughout this entire work has been to avoid the historical view-point, as much as possible, and to confine ourselves strictly to the business in hand; namely, constructional principles and their application.
The pneumatic principle has been adopted in all the piano-players that we have occasion to survey, and its application has been in all cases essentially similar. Indeed, the two schools of construction differ, not in the application of the pneumatic principle, but in certain details of construction, which are important but not vital. One general description will be quite sufficient to acquaint the reader with the make-up of these instruments, and it will be easy to undertake any further explanations of important variations.
The underlying idea, upon which the whole player is built, may be described as arising from the knowledge that a bag or bellows of suitable material will collapse whenever the air is exhausted from it, and become inflated again when the air is permitted to rush into it, which happens as soon as the vacuum is destroyed. Now it is obvious that here, in these two processes, we have the possibility of producing a reciprocating motion, and the value of this is evident when it is remembered that the process of pianoforte playing, when reduced to its lowest terms, is essentially the combination of the alternate manual motions required to depress and release a key. Consequently, the matter of designing a pianoforte-playing machine is reduced to the problem of placing a bellows over a key, or in mechanical connection with it, in such a way that the inflation and deflation of the bellows will operate levers to depress and release the key. Thus far, it may be understood, we are dealing with elementary mechanical principles. But the questions arising from consideration of the control of these bellows are far more delicate, and require for their solution a high degree of mechanical talent. Let us see how the problem has been worked out.