Even tone is another most difficult object to strive for in playing scales, for the human hand is physically so constituted that certain of the fingers are weaker than the others, namely, the 4th and 5th are the weak ones, and the 1st, 2nd and 3rd the strong ones. From this fact ensures the natural consequence that the notes struck by the 1st, 2nd and 3rd fingers are liable to be louder and firmer in tone than those upon which 4th and 5th fall.
This weakness can only be corrected by pressure from the forearm transmitted to the fingers, as I have already insisted upon when speaking of the articulation in five-finger exercises. The pressure is here used as an equalizer, in this fashion, that the conscious habit of the pressure having been established by practice, it works upon the mind and forces the performer unconsciously to give an extra compensative pressure to the weaker fingers, according as he detects by his ear that they require it.
This equalizing of the tone by pressure serves again to illustrate how the theory of its administration through the forearm, working upon the fingers, establishes absolute control of the muscles, not so much by its direct action on the fingers as by its indirect stimulus to the mind, which through it becomes conscious that it has work to do, and is alert to command the muscles properly.
Later on it will be seen how vital a part of piano technique this control of the muscles by the mind is, constituting, as it does, the principle upon which is based the imparting of light and shade, gradations of expression and tempo, in fact the life which changes the sounds of the mechanical instrument into music.
Scales should be played every day and in all tonalities. Upon the black notes the fingers may be slightly extended, as it will be found difficult to keep them quite as rounded as on the white ones, owing to the lack of space. Finally, it is important in practicing scales that they should be played absolutely correctly, therefore it is always best to practice each hand separately.