ISIr. Hunt on. the Cinephantic Colour 2'op. 253 



by a string drag, and thus ditfereut from that of the coloured disc. 

 The writer at once perceived the possibility of obtaining an endless 

 variety of beautiful effects with these differential motions, and having 

 a small colour top, he had a perforated loose disc made ; but without 

 proposing to do more than realize, for his own amusement, what he 

 understood to have been already exhibited. The first experiment failed 

 to produce any efiect worth looking at, but induced a more seai'chiug 

 consideration of the conditions necessary to success. The writer next 

 thought the London top had probably been made to reproduce some of 

 the effects shown to the Glasgow Philosophical Society by Mr. Rose, in 

 April, 1858, but with the addition of colours ; at any rate, he in a little 

 time succeeded in reproducing these effects. He also produced other 

 beautiful and to him quite new effects ; and ultimately found that he 

 had carried out his experiments in a direction differing considerably 

 from that taken by Mr. Gorham. This was not much to be wondered 

 at ; for the elements of the experiments, simple as they are, are so pro- 

 lific, in number and variety, of optical effects, that it would have been 

 more surprising had two persons, working independently, happened to 

 have pursued the same track. 



In Mr. Gorham's experiments, the first effect to be noticed was the 

 multiplication of the colours on the top, as seen through the perforated 

 disc. A simple example of these colours comprised three sectors, 

 respectively tinted violet, green, and scarlet. When the top was spun, 

 and before the loose disc was added, the three colours were merged into 

 a single compound tint ; but when seen through the loose disc, thg 

 colours appeared separated and repeated in five groups, every group 

 comprising the three colours in the reverse order to that of their actual 

 arrangement on the top. The next effect to be noticed was the multi- 

 plication of the perforated devices. The repetition of the colours arose 

 very simply, and depended on the ratio of the velocities ; it was, how- 

 ever, difficult to explain without a diagram. As to the multipUcation of 

 the perforated devices, the writer gives what he believes is the true 

 explanation, observing, however, that it is not that of the inventor, Mr. 

 Gorham, which last will be found in the work already referred to. The 

 central aperture of the loose disc is made slightly larger than the dia- 

 meter of the top spindle, and the latter acts like a pinion, gearing into 

 an internally-toothed wheel — the wheel being represented by the edge 

 of the disc aperture. If the disc is prevented from turning, but held 

 free, every point will describe a circle of minute radius. If the disc is 

 now allowed to turn round, but not as fast as the top, the circles will 

 be converted into cycloidal curves. To demonstrate this, a number of 

 white points were put upon one of Mr. Gorham's discs, and a black 



