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THE POPULAR EDUCATOR. 



Then comes a remarkable statement, page 270: "It is 

 obvious that if, instead of a mirror, another person whirls 

 round in an opposite direction, and with the same velocity, 

 a similar disc, the effect will be the same." 



No motive effeats can be more dissimilar ; the second disc 

 multiplies the fig-area, and makes anamorphoses (shapeless 

 forms) of them. The last sentence convinces one that neither 

 Sir D. Brewster nor Dr. Lardner have devoted much thought 

 to the subject, otherwise they would have seen that, merely for 

 the purpose of dispensing with the mirror, there is a much 

 more satisfastory way of using the second disc. 



an inch ; whilst that of the larger pulley which, of course, 

 moves slower, and carries the perforated disc, having, say, 

 four slots or openings is one inch and three quarters. When, 

 the wheel is turned, the bands, one of which is crossed, cause 

 the two pulleys, one bearing the device and the other the 

 perforated disc, to go round in opposite directions ; and, on 

 looking through the slots, the operator sees the curious changes 

 that occur : for instance, a piece of cartridge paper, six inches 

 square, is painted with diagonal lines, as shown in Fig. 3, so as 

 to have alternately green, white, red, white, green, white, red, 

 and so on. When this is attached to the asle of the small 



Connect the disc of devices to the perforated disc by means 

 of a brass rod (Fig. 1) ; let this rod pass through the disc, so 

 that its ends may rest on a crutch support. Set the discs 

 revolving in the same direction, and, looking through the slots, 

 yon will see the figures in motion precisely the same as in the 

 mirror. How this very obvious contrivance did not occur to 

 them, it is difficult to say. 



The apparatus so clearly described by Mr. Rose has been 

 constructed in a very cheap form by the Rev. Mr. Pilkington 

 (Fig. 2). ' Oa a turned wooden pillar and stand is fixed an elbow- 

 shaped iron, carrying the axles, one of which work inside the 

 other. Each axle carries a pulley, round which the two bands 

 or strings are placed ; the strings pass round the grooved wheel 

 and handle for giving motion to the two discs, which move in 

 opposite directions, and at unequal velocities, by crossing one of 

 the pulley bands. The diameter of the small pulley attached 

 to the device, the axle of which works inside the other, is half 



pulley, and the disc with four apertures to the larger one, and 

 the wheel turned in opposite directions, the diagonal lines change 

 in the most curious manner, and produce the symmetrical 

 pattern shown in Fig. 4, the letters of which, corresponding 

 with the first letter of each colour, show the manner in which 

 the pattern is tinted with them. 



The supporting pillar of this cheap form of the kalotrope 

 stands twelve inches high, and screws or drops into a turned 

 wooden foot, four inches in diameter, and an inch thick, which 

 should be loaded with lead to make it stand quite steady. The 

 turning wheel works on a screw, which attaches it to the pillar, 

 and is three inches in diameter, having two grooves sunk three- 

 eighths of an inch, in which the two bands elastic letter bands 

 work. The elbow piece of brass is screwed in above the driving- 

 i wheel, and projects horizontally one inch and a quarter, and is 

 the same in height, with a crutch at the top to carry the two 

 axles, working one within the other, of which one end rests on 



