254 Mr. Hunt on the Cinephantlc Colour Top. 



disc was placed below, to prevent the interference of the colours that 

 would otherwise be seen through the perforations. On repeating Mr. 

 Gorhana's experiuient with these alterations, a variety of cycloidal 

 curves were delicately traced by the white points, and with such rapi- 

 dity as to appear continuous round the disc. Near the centre the 

 curves were looped ; further out, cusped ; and at the outside, undulated. 

 The best effect was yielded where the points moved in the cusped 

 cycloidal path ; and on considering the motion of each point in the 

 curve generated in the manner described, we find it vai'ies, being most 

 rapid at the middle of each hollow, and gradually becoming slower, 

 until at the cusp it is momentarily at rest. Afterwards the motion as 

 gradually increases again, and so on. Now, whilst the motion of any 

 part of the device is rapid, the impression on the eye is comparatively 

 faint and indistinct, particularly if contrasted with that received when 

 the motion is for a moment neutralized. The eye, in fact, only appre- 

 ciates the impressions made at intervals corresponding to the cusps 

 of the curve, and these impressions are extremely well defined, and, 

 with well selected devices, form very pleasing combinations. The 

 images, as it were, experience a species of pulsation during their 

 motion, and each impression is charged with the colour which happens 

 to be beneath the perforation at the instant ; whilst the number of 

 impressions depends on the number of curve cusps in the circle. 



The first of Mr. Rose's effects produced by the writer was that of 

 apparent rest whilst the discs were in rapid motion. The loose disc 

 had six apertures, with equal openings and intervals. Various series of 

 coloured sectors were placed on the top, and when the proper ratio of 

 velocities was obtained, five apparently stationary repetitions of the 

 series were seen. This experiment was first tried on a small scale, and 

 various peculiarities were observed, which led to further experiments. 



The next effect sought for was that of the rotatory or other motion 

 of details, in a series of apparently stationary circles, arranged in a ring 

 roimd the top. This presented considerable difficulty ; but was finally 

 obtained by means of strongly contrasted colours, and by confining the 

 brightest to a comparatively small sector. The loose disc was per- 

 forated with twelve circles, a small circle or ball being left in each. In 

 one circle, the ball was at the point furthest from the centre of the 

 disc ; in the next, a twelfth round ; in the third, two-twelfths round, 

 and so on. Mr. Rose showed a similar device in black on white, and 

 he produced the effect by Ulumiuating the eutii-e disc at (rapid) inter- 

 vals, between which the cii'cles, owing to the disc's motion, took each 

 other's places in succession ; so that if the eye was fixed upon the appa- 

 rently highest circle, the actual successive change of the several circles 



