120 Professors Perry and Ayrton on the Music 



of the machines can a sudden change be produced in phase. 

 Now it is obvious that we require a motion-producer of far 

 greater range than any of these, if we are to play on the 

 emotions, since all the qualities — elation and depression, velo- 

 city, intensity, variety, and form (which it is considered are 

 possessed by a complex emotion) — must be visibly rendered. 



The result produced by our instrument is this : — A round 

 shadow is thrown upon the plain white wall of the room in 

 which the audience are seated. The shadow appears to be a 

 large black ball, of which the size during the performance may 

 be made to vary. It has motions over the wall which are pure 

 harmonic or combinations of harmonic motion, produced by 

 our being able to give to the shadow two independent motions 

 — one in a vertical line, the other in a horizontal line, each con- 

 sisting of a combination of linear harmonic motions, the ampli- 

 tude, period, or phase of any one of which may be varied at will. 

 We give a collection in figures (A to U, Plate V.) of some of 

 the most simple paths traced out by our moving ball, and which 

 differ from the ordinary Lissajous' figures in that we have 

 placed little circles at such distances asunder as are passed 

 over in equal times, in order to give an idea of how the velocity 

 varies at different parts of any such path. Unfortunately, 

 however, for giving a conception of the appearance, it is this 

 variation of velocity, the effect of which on the senses no figure 

 or description can give any idea, which constitutes one of the 

 most striking features of the exhibition. Many of our readers 

 will, however, have seen the motions of a very large Black- 

 burn's pendulum, and of a very long simple pendulum ; and 

 they will therefore have gained such an idea of the motions of 

 which we speak as a person, who has heard only the chirp of a 

 sparrow, has about Beethoven's sonatas. 



It must be remembered that while all the possible paths of 

 the moving body are beautiful in shape, they are also endless 

 in their variety. Not only may they vary without limit in 

 their form, but also in their size, and in the velocity with which 

 the body moves along them. Thus, perhaps the body is swing- 

 ing slowly in a straight line in any direction, like the swaying 

 of a huge tree in the wind, or so rapidly that a dark line only 

 is visible, when, touching a key, the line is suddenly seen to 

 open out, and the body rolls round a small or great circle, or 

 a small or great ellipse of any proportions and with any velo- 

 city*; or the figure may be like any of the simple figures 



* One of the most beautiful things in connexion with the recent monster 

 captive balloon in Paris was its rolling round and round in the breeze, 

 like a huge inverted conical pendulum, after the stay ropes had been 

 liberated, just before its ascent. 



