of Colour and Visible Motion. 119 



nates. Similarly, the emotions produced by the play of 

 colours in a fine sunset, by the rolling of the waves on the sea- 

 shore, by the rhythmic motion of a large engine or of a long 

 pendulum, by the tracing out of the combined harmonic curves, 

 which have now become well known to all who have heard 

 lectures on vibrating bodies, seem to be quite different from 

 one another, and from the emotions produced by sound. 



We have therefore tried to make a machine which to the 

 emotions produced by a combination of colour, a mass in 

 motion, and by motion in curved paths, would bear the same 

 relationship as a musical instrument to music. We have not 

 ventured to give our machine a name, since the name of the 

 instrument should be that of the art ; and although we have 

 a name for exciting emotion by sound (music), we lack names 

 both for the art of exciting emotion by colour, and by moving 

 bodies. 



Many instruments have already been devised for combining 

 together two harmonic motions ; but as the conception of using 

 such machines as emotion-exciters has never been present in 

 the designers' minds, the performances of these instruments, 

 although very beautiful, are necessarily of a comparatively ele- 

 mentary nature. The most important of these machines, all of 

 which, with the exception of one or two Prof. Guthrie has been 

 so very kind as to have arranged in working order before us, 

 are Blackburn's pendulum, Wheatstone's kaleidophone, Lis- 

 sajous' tuning-forks, Yeates's vibrating prisms, DonkhVs har- 

 monograph, Tisley 's and Spiller's harmonograph, and Hopkins's 

 electric diapason. In some of these, as in Blackburn's pen- 

 dulum, only one particular pair of harmonic vibrations can be 

 combined, and any change in the period of either means a stop- 

 page of the instrument, corresponding in music with a delay 

 in the tune at the end of every chord ; in others we can change 

 the period of one or other of the component harmonic vibra- 

 tions, but have no certain means of controlling the amplitude, 

 which in music would be equivalent to an inability to render 

 at will a note forte or piano ; or, rather, as it is not only the 

 strength of the entire note, but even the amplitude of the 

 various component harmonics that these instruments cannot 

 regulate, it would be as if in music there was the probability 

 of a note marked in the score as piano for the flute being ren- 

 dered by a loud blast on the trumpet. In only one of these 

 harmonic-motion compounders with which we are acquainted, 

 viz. in the most perfect of the existing ones, Tisley's harmo- 

 nograph, can an elliptic and a linear motion be combined; 

 but even in this case a change from this motion to any other 

 can only be made by first stopping the machine ; and in none 



