850 Description of the Kaleidophone, 



No. 3. When this prismatic rod is put in motion, in the 

 direction of either of its sides, the points move only rectiUneally, 

 but when the motion is appUed in an obhque direction, a variety 

 bf compound curves is shown ; this rod is principally employed 

 to exhibit the optical phenomena, which will be afterwards 

 mentioned. 



No. 4. When a rod is straight, the curve produced by any 

 point describing its motion, is always in the same plane ; but 

 in a rod bent to any angle, the two parts moving most frequently 

 in different directions, curves are produced whose parts do not 

 lie in the same plane. A few trials will soon indicate the best 

 way of applying the motion, so as to cause the two parts to 

 ;Vibrate in different directions. 



Before the conclusion of this subject, I will avail myself of 

 the opportunity of observing, that the application of this mode 

 of experimenting may be extended to the dehneation of every 

 description of curvilinear and angular motion, when the am- 

 plitudes of the tracks are not too great ; and by this means, it is 

 not improbable that the experimental knowledge of many inter- 

 esting principles in science may be facihtated. 



On the Duplication and Multiplication of Objects. 



When dark objects are substituted for luminous ones, their 

 tracks become nearly invisible, and from the longer duration of 

 the visual impression at the hmits of vibration, the images 

 are multiplied in proportion to the number of points at which 

 they are retarded. Place horizontally on the rod No. 2, a 

 word printed or written on a piece of card ; in the lowest mode 

 of vibration, at the opposite limits of the excursions, two legible 

 images of the word will be distinctly seen, and but an indistinct 

 shade, occasioned by the tracks of the letters, will appear in the 

 intermediate space : the vibratory motion is imperceptible to the 

 eye ; the images will, therefore, appear stationary in this respect, 

 but the diminution of the excursions will cause them to approx- 

 imate very slowly and gradually towards the centre : this 

 diminution operates so gradually, as to allow the images to 

 superpose each other completely at each recurring vibration, 

 without producing any intermingling or confusion. 



On placing the object perpendicularly, the two images will 



