194 



THE POPULAR EDUCATOR. 



coloured top), and a number of perforated black discs for the 

 front wheel, similar to the opaque disc of a coloured top, with a 

 slice cut out to show the changing effects. The instrument 

 could be used to show simple persistence of vision by merely 

 removing the front perforated black disc ; as, for instance, the 

 re-composition of the colours forming white light by the rapid 

 rotation of a disc bearing the prismatic colours, when each 

 colour is presented to the eye so nearly at the same instant that 

 proximate whiteness is produced. By rotation of a disc having 

 alternate sections of two colours a third was produced, as 

 imitated in the colour-top ; thus red and blue, by rapid alter- 

 nate presentation to the eye, produced a purple spectrum. 



Again, a disc charged with black balls nearly in contact pre- 

 sents under rotation a shaded solid ring, dark in the centre, 

 where the balls are close together, and light at the edges, where 

 the white interstices increase in breadth. 



For the true kalotrope effects the two wheels are used ; and in 

 1855 the inventor was kind enough to give the writer the follow- 

 ing valuable information with regard to the discs to be used 

 and devices best adapted to the kalotrope. 



The Kalotrope Discs. Mr. Rose claims the merit of suggest- 

 ing variety in the perforated discs, which, combined with diffe- 

 rent velocities, produces those illusions which make the kalotrope 

 an optical arrangement different from any other that preceded 

 it. But he prepared at first only three discs, the first having 

 twelve slots, the second having twenty-four slots, and the third 

 divided as in Fig. 12. This last consists of three concentric 

 circles ; the first has forty-eight slots, the second thirty-six 



slots, and the third twenty-four slots. Thus in every inch the 

 multiplications, combinations, involutions, etc., vary. 



The Range of Effects by the Kalotrope. Every disc of devices 

 will not with advantage bear all the varieties of action of which 

 the apparatus is capable. But it may servo to indicate the wide 

 range of effect producible by the apparatus to mention all the 

 varieties to which any one disc might be subjected. 



It may be shown (1) under simple persistence ; (2) with the 

 second wheel playing over it, without any perforated disc ; (3) 

 with disc of twelve slots ; (4) with disc of twenty-four slots ; 

 (5) with disc of three circles of slots. Under these five con- 

 ditions it may be combined with variations of velocity, and also 

 variations of relative velocity of one wheel to the other. 



Now although some of these variations would not be appre- 

 ciated by a sight-seeing audience, there is scarcely one that is 

 not fraught with instruction for the student in optical science. 



The Series of Discs of Devices. The series of discs prepared 

 by the inventor were simple and unartistic, and are not in every 

 case the best devices for the intended purposes. His views 

 expanded as he proceeded in the arrangement of the apparatus, 

 and hence, as the idea was not at the first present to him in all 

 its unity, there is necessarily some want of coherence of plan 

 and adaptation in the details. Indeed, the main object ho had 

 in view was to analyse disc action, ascertain its capabilities, 

 and give examples of action just sufficient to indicate a highly 

 useful and interesting apparatus. The kalotrope may be per- 

 fected by artistic ingenuity in the construction both of the 

 devices and the perforated discs. The inventor merely claims 

 to have laid down a principle in an intelligible and workable 

 form, and to have produced a working model quite sufficient as 

 a guide to any one who would take up the kalotrope and produce 

 it under the best auspices. 



The discs are two feet diameter. The first (Fig. 13) contains 

 twelve circles, about three inches diameter, round its margin, 

 painted with intense black. The effect of this disc has been 



already described as a ring a ring divided into twenty-four 

 sections, twenty-four ovals, forty-eight involuted figures a com- 

 pound involuted figure. 



The second disc (Fig. 14) is a bold and simple thaumatrope 

 device of rings and interim balls, with ~ther moving details. It 

 changes to forty-eight involved rings, xall of motion, and again to 

 a compound involu- 

 tion of much beauty. 



The third disc (Fig. 

 15) is a black ball 

 within two black con- 

 centric circles : re- 

 volving twenty times 

 per second, it is lost. 

 The apparatus gives 

 mathematical data 

 in regard to the phe- 

 nomenon ; the ball 

 changes its place 

 every 600th of a se- 

 cond, and returns 

 upon the eye in the 

 same point every 

 20th of a second. - 

 Thus far it is shown 

 by the single wheel 



under simple persistence. Next, screw on the second wheel and 

 the twelve-slot disc, and turn at twenty per second, when 

 twenty-four black balls will be visible. In this case the ball 

 changes its place every 1,200th of a second, and returns to any 

 given point every 20th of a second. This experiment shows how 

 powerfully the eye is affected by rapid alternations of apparition 

 and disappearance. 



It is a fact worth naming that if a person can get the habit 

 of winking very rapidly, ho can impress the eye with a light of 

 great intensity by looking at an ordinary gas bat's-wing burner. 



The fourth disc is a white ball in an intensely black circle (Fig, 

 16). With a speed of twenty per second this ball cannot be lost, 

 but will be a visible white circle over the black one hence the 

 greater impression made on the eye by whiteness. Taking the 

 second wheel and twelve-slot disc, twenty-four strong white balls 

 are seen ; then take the twenty-four slot disc, and forty-eight 

 white balls will be visible ; thus showing that a white ball may 

 change its place every 2,400th of a second, and return again to- 

 the same point every 20th of a second, and be visible by inter- 

 rupted vision. 



In both these experiments all the balls appear and disappear 

 alternately at the same instant ; but in the first experiment the 

 interval of passage from slot to slot is 480th of a second, 

 and in the second experiment 960th of a second intervals, of 

 course, too brief to be appreciated by the eye. 



The fifth disc is a circular arrangement of spectrum for 

 composing white light, 

 merely introduced as 

 the simplest effect of 

 persistence, and as a 

 starting-point in the 

 illustrations. 



Qth Disc. Nine 

 parti - coloured stars,- 

 with falling aerolites, 

 simply to show the 

 first elements of cir- 

 cumferential revolu- 

 tion, when the twelve- 

 slot disc revolves in 

 front of them. 



1th Disc. Four cir- 

 cles of balls, number 

 different in each circle- 

 to show the principle 



on which circumferential motion is accelerated fewest balls 

 move the swiftest. This disc may be used with different per- 

 forated discs, and the wheels moved with different velocities, by 

 which means figures are multiplied by persistence and singular 

 varieties of motion are observed. 



8th Disc. Nine bold rings with interim action, to be sub- 

 mitted to all the perforated discs in succession, when remarkable 



