238 ANNUAL OF SCIENTIFIC DISCOVERY. 



made with great facility ; and when the pictures are united, the effect is ex- 

 cellent. 



THE KALOTROPE. 



Rev. T. Rose, of Glasgow, communicates to the London Athenaeum the 

 following description of a new instrument, an improvement on Prof. Quet- 

 etet's Thaumatrope, which he calls a " Kalotrope " : 



The kalotropc exhibits to an entire company the well-known illusions of 

 the Thaumatrope, but its claims to be considered a perfectly new optical ar- 

 rangement rest in a peculiarity of action by which a number of illusive 

 changes are brought over any one disc of devices. The mechanical construc- 

 tion of the apparatus consists of two concentric wheels, to which a consider- 

 able range of velocity is given by a series of wheels and pulleys. They 

 move in contrary directions the one wheel (the hinder) carrying the disc 

 of devices ; and the front one carrying a disc with radial perforations, diffcr- 

 ing in number and character. To understand the effect, AVC must have 

 regard to the angular motion of the perforations through which alone the 

 devices can be seen. Now it is obvious, that if the devices were at rest, and 

 the perforations only moved, the latter must pass over a space equal to the 

 full breadth of the figures in order to clear them ; but since the devices and 

 perforations are both moving, and in contrary directions, the devices are 

 nan-owed in one of their diameters in proportion to the relative velocities of 

 the wheels. But whilst the dimensions of the devices are measured to the 

 eye be the relative motions of the wheels, their number is dependent solely 

 on the number of perforations in the front disc. Hence arises an almost 

 indefinite field of illusion, in the way of multiplication, combination, involu- 

 tion, and intricacy of motion. I have prepared an extensive series of discs 

 to bring out these effects. The kalotrope is not, however, confined in its 

 action to merely pleasing illusions ; it likewise offers valuable scientific illus- 

 trations in regard to the intensity and duration of spectra, the measure of 

 persistence, and certain remarkable properties of complementary color. I 

 think the kalotrope is a device which may be recommended to the drawing- 

 room for its beautiful effects, and may prove of value in the lecture-room as 

 an exponent of scientific truth. 



THE OPTHALMOSCOPE. 



An instrument called the Ophthalmoscope, by the aid of which the human 

 eye may be internally examined, has recently been brought to the notice of 

 the scientific world. The instrument is in the form of a concave mirror, 

 with a hole in the centre, in which a lens is inserted; to this another lens is 

 added which, however, is separate and movable. When the instrument is 

 used, a lighted candle is placed by the side of the patient. The concave 

 mirror is then held in front of the eye to be examined, while the movable 

 lens is suspended between the light and the mirror in such a manner as to 

 concentrate the rays of the first on the second. The reflected rays converge 

 on the retina, and on passing through it diverge and render luminous the 

 whole interior of the eye, which the observer can see by looking through 



