of Colour and Visible Motion, 125 



therefore revolving with it, a sort of double wheel of metal of 

 the form shown. 1 1 is the pulley round which the cord passes, 

 if it is by means of a cord that we sum the harmonic motions ; 

 or the pulley may be absent; and the axle of the pulley is then 

 simply a crank-pin. Then the rate of revolution of the shaft 

 A determines the period, the distance of the axle F Gr from the 

 shaft the amplitude, and the position of F G relative to a fixed 

 diameter K L the epoch of the component harmonic motion. 

 By shifting, then, the axle F G we may alter the epoch for 



IT 



any multiple of j for the greater amplitudes, and of ~ for th e 



smaller. As there is, however, only a limited change of epoch, 

 we think, on the whole, that our improved roller method is to 

 be preferred. 



We have used combinations of pure harmonic motions for 

 obvious reasons ; but it is possible that,, instead of each section 

 of the roller giving a pure harmonic motion, it may be found 

 more suitable to have it giving some other kind of periodic 

 motion ; and such an instrument will differ from the preceding 

 in pretty much the same way that one musical instrument 

 differs from another. As various means have already been 

 devised, by revolving sheets of parti-coloured glass, for pro- 

 ducing the effects of the chromotropes of the magic lantern, 

 which physiologists have informed us produce such marked 

 and instantaneous effects on the nervous constitution, and phy- 

 sical organs, of children, we have not yet specially turned 

 our attention to the mechanical details of the colour portion 

 of our machine. 



In what has preceded we have spoken only of projecting the 

 motion of a single ball on a wall ; but there is no reason why 

 the motions of several balls should not be gazed at simulta- 

 neously, nor why the people of a large city should not have 

 an exhibition of the colour and motion art upon a canopy of 

 clouds on a dark night. 



For assistance rendered us during the construction of this 

 apparatus, and for the general intelligent interpretation of our 

 wishes, we have to thank our late assistant, Mr. Kawaguchi, 

 one of the brightest of the students of the Imperial College 

 of Engineering, and one whose constant earnestness of pur- 

 pose, while it rendered his life the more valuable to the scien- 

 tific development of Japan, now makes his recent death the 

 more to be deplored. 



Phil. Mag. S. 5. Vol. 7. No. 41. Feb. 1879. 



