119 



there is another of the same series bearing to it the 

 ratio f , each tone of series 4 will bear to some tone of 

 series 2 the ratio |f, and will therefore serve as a leading 

 note in melody to the latter tone of series 2 ; and it is 

 more convenient to consider each tone of series 4 as con- 

 nected with that tone of series 2 to which it bears the 

 ratio |f. For instance, g$ is the major third of e ; it is 

 also the leading note of a, and is considered as connected 

 with a. 



Each digital of the fourth series is therefore placed 

 immediately before that of the second series to which it 

 has the relation -j-f. As the lower third of the length of 

 each digital of the second series is immediately preceded 

 by a prime seventh, it saves space to extend the digitals 

 of the fourth series only to two-thirds of the length of 

 those of the second series. The digitals of the fourth 

 series, then, are disposed as in the diagram. 



The relative width of the various digitals is to some 

 degree a matter of convenience, but that adopted by Prof. 

 Poole has some practical advantages which will appear 

 when we consider the completed key-board. 



There are in the horizontal line of any key ten digitals ; 

 four of series 1, three of series 2, one of series 3, and 

 two of series 4. The octave is divided into twenty-four 

 spaces, and of these, three are given to each key-note and 

 two to each of the other digitals. It has been found most 

 convenient to elevate the digitals of the second and third 

 series half an inch above those of the first, and to elevate 

 those of the fourth series one-fourth of an inch above 

 those of the first. All the digitals of each series are in 

 the same plane, but the whole key-board is inclined 

 slightly upward towards the back. Accompanying are 

 a plan and section of an octave of the full key-board. 

 This diagram gives all keys perfect from Cj, to ~Fst. Blue 



