A very valuable chart is one showing contemporaries, in musical and general history, also parallel events, for example, the musicians who lived in a certain century, famous kings, statesmen, explorers, poets, scientists, discoveries (such as America, printing, etc.), famous battles, events in Biblical and American history, and other political events of the same century. Credit should be given in class standing for these charts. LESSON XXV. THE EVOLUTION OF THE PIANOFORTE. While the violin, on account of the simplicity of its construction, arrived early at a stage of perfection, the complicated mechanism of the pianoforte required many generations and many scores of more or less successful experiments to attain anything like a corresponding plane. Indeed, such experiments are still constantly in progress; so that the pianoforte of the future may conceivably realize possibilities as far ahead of the present piano as that is ahead of its predecessors. The first attempts at piano manufacture, however, had little in common with our modern pianos, save the principle of the combination of the keyboard with strings; since in construction and resulting tone few points of similarity exist. =Clavier a Substitute for the Organ=.—We are probably indebted to the extensive use of the organ for the earliest combinations of keys and strings. As the demand arose for a more conveniently-keyed instrument than the large church organs, for practice or private houses, small portable organs were invented; yet even these did not satisfy the want entirely, owing to the _difficulties in their wind supply_, which required an assistant as blower. Thus the organ keyboard came to be applied, as early as the 11th century, to already existing stringed instruments which were adapted to the purpose. =Two Classes=.—There were two classes of these, each made on the principle of the zither: namely, by stretching strings over a flat surface or box, generally across bridges, this box serving as a resonator, to reinforce the weak tone of the strings. One such instrument, in which the strings were _struck by_ little wooden _hammers_, was called the Dulcimer; another, in which the strings were sounded by _plucking_ with the fingers or by a quill, was called the Psaltery; and from these two were developed the earliest instruments of the piano class, called by the general name of “Claviers,” from _Clavis_, a key. The dulcimer type resulted in the =Clavichord=; the psaltery type in the =Harpsichord=, and, although many other names were given to varieties of these instruments, all may be placed in one of the two classes of which they are the chief representatives. [Illustration: CYMBALUM OR DULCIMER.] [Illustration: PSALTERY. This instrument also came in square and other forms; strings varied from 6 to 38.]