SOUND 265 



(b) All the notes are audible ; more so than with forks. 



(c) Any note within the speaking range of the boxes can 

 be added at any time for a few shillings. 



(d) Any interval can be changed for any other (so far as 

 notes are provided) in half-a-dozen seconds. A complete set 

 would comprise a lower c (for tenths and twelfths), two c's (for 

 unisons and beats), and the diatonic scale from c to c. 1 A 

 convenient * small ' set would be the four notes of the common 

 chord, with a duplicate of the lower c. This will give unison 

 and beats, third, fourth, fifth, and octave. 2 



(e) There is absolutely no trouble in manipulation. Any- 

 one blowing the bellows, and having adjusted the pencil of 

 rays once for all, the demonstrator has only to substitute 

 notes as required, and manipulate a pinch-cock. If the pencil 

 is awkward to manage, a black card with a circular aperture 

 may be interposed between the first mirror and lantern, 

 to confine it within bounds. The mirrors are so near 

 each other, that little light is lost, and the projection is 

 brilliant. 



(/) The angular motion being great, the figure is on a 

 large and bold scale. 



(g) Most important of all : the notes can be tuned in 

 operation, with the greatest nicety. There is no tiresome 

 tuning, or loading with wax. The pitch varies with the 

 wind-pressure^ within more than sufficient limits, and the 

 hand on one or other of the pinch-cocks on the tubes will 

 either keep any phase of the figure ' steady,' or cause it to 

 pass through the transitional forms with any rapidity 

 desired. 



With this apparatus, Lissajous' figures become a delight- 

 fully easy and effective projection. 



1 For audibility, however, a range of notes from G to G is better than C to 

 c, and this scale was therefore adopted. 



2 We have some hopes of still further simplifying the apparatus by making 

 one of the reeds variable in pitch by a rack-work ; but the experiments on 

 that point are not concluded at the date of this. 



