THE KALEIDOSCOPE, ETC.] 



UNDTJLATORY FORCES. LIGHT. 



77 



course enclosing a cavity, which may be filled with a 

 refracting liquid. This may vary from distilled water 

 to strong hydrochloric acid, the latter having a strong re- 

 fractive power, and also a peculiar action on the rays of 

 heat and light. In naming this, we may presume that the 

 majority of our readers will not have the opportunity of 

 trying experiments on the large scale : we may, however, 

 suggest the employment of two watch-glasses, or other 

 glasses of large size, properly joined together, BO as to 

 hold a fluid. By such an arrangement a great variety of 

 interesting results may be obtained ; and, by a little 

 patience, the student will greatly enlarge his knowledge 

 of the effects of various liquids on the dispersion and 

 refraction of the forces of light and heat. Any ordinary 

 single or double convex lens answers the purpose of both 

 a magnifying and burning-glass ; one of the simplest of 

 the kind being small blown-glass globes tilled with water, 

 which are often sold in the streets for employment of a 

 microscope. It may not be out of place here to warn 

 our readers of the risk run when water-bottles, or 

 some kinds of window-glass, are in snch a position that 

 they can concentrate, lens fashion, the rays of heat and 

 light. In the manufacture of crown glass, a thick piece 

 is generally left in the centre of the plate, which, if 

 suitably placed, will act as a lens. If either a water- 

 bottle, or such a piece of glass, happen to be at their 

 focal distance from any inflammable substance, it may 

 just occur that they may bring the rays of the sun to 

 a focus thereon. By such singular means toilette t 

 have been set on fire, ami much destruction of pro] 

 lias ensued. Granaries and warehouses have. in a similar 

 manner, suffered through this lens-like glass placed in 

 the windows. These instances show how desirable it is 

 that a general knowledge of scientific laws shoii: 

 spread as widely as possible. 



TIIK K U.KIDOSCOPE. 



TUB kaleidoscope, to which we shall first direct attention, 



was invented by .Sir David Brewgter; and has, for r. 



years, been a source of pleasure and n: 



to the infinite variety and beauty of the forms H 



to the eye. 



Externally it has the form of .1 cylit, ' which 



are placed pieces of looking-glass, which act as re- 

 flectors. At one end of the instrument is nn 

 through which the observer looks ; and ;r ; is a 



piece of ground glass, on the ii" t the 



objects, which may be small pieces 1 glass, or 



other coloured and transp.-i posi- 



tion the latter may be placed, they are continually and suc- 

 cessively reflected by means of the mirrors; and i 

 any single object will undergo retl< 

 own surface, and then from its image in one of tin' 

 mirrors to that placed a: .to. The r 



is, that, with several littl. M immense variety of 



: .Minced: and the slightest chan 



their position instantly produces a change of form in 

 the design. This, whilst being an essential i ! 

 the instrument, and productive of the 

 results, detracts from its value in an artistic point of 

 view, a* we shall explain when describing the Debusscopc. 



THE DEBUSSCOPE. 



THIS ingenious contrivance is constructed on similar 



principles to those involved in the kaleidoscope. It, 



however, has the advantage of presenting permanently 



the patterns and forms it produces ; and hdico may be- 



reat use to manufacturers and others who may 



avail themselves of it, in order to design patterns. 



, of two re8ectors, set at an angle with each 



r . between which, the object whose appearance is to 



be multiplied is pla< ssivo reflections produce, 



from the most li ms object, the most pleading .-"irl 



lar results. Tims, a piece of paper on which the most 



Mar scrawl may be drawn, will, owing to the com- 



f the rough ilr-i rn, produce a pattern of a most 



pleasing character. Even a piece of string, carelessly 



placed between the reflectors, may be made to assume 

 any variety of form, and, simultaneously, to produce an 

 equal variety of designs. Instead of having "to look 

 tlirough the instrument, as in the kaleidoscope, the ob- 

 server simply has to look on it between the two reflec- 

 tors ; and hence convenience and permanency are at 

 once obtained. When the Debusscope becomes fully 

 known, there is no doubt but that it will be highly 

 valued. We are indebted to M. Debus for its invention ; 

 and hence its name. 



THE THAUMATROPE, PHANTASMASCOPE, 

 AND ROSE'S KALOTROPE. 



IN the earlier part of this section* we referred to the 

 fact, that light travels with such speed as not to permit 

 the eye to observe successive impulses on the retina, if 

 such are more frequent than about eight in a second. 

 Thus, the spokes of a wheel, if in rapid motion, present 

 an indistinguishable appearance to the eye. If, however, 

 a strong light is cast on them instantaneously, they will 

 appear, for tho moment, quite stationary ; even the act 

 of suddenly shutting and opening the eyes will some- 

 times afford the same result. 



By means of mechanical arrangements this principle is 

 capable of many interesting applications, in which what 

 is termed the persistency of vision is employed, together 

 with an intermission of tight passing from the object to 

 the eye. Generally speaking, the object is caused to 

 revolve rapidly ; and, by means of suitable contrivances, 

 its surface dy, but rapidly, exposed or shut off ; 



and so tho effects of the thaumatrope, <kc., are produced. 

 Vig. 86. 



The thaumatrope, illustrated in the above cut, is made 



by painting, on <t sides of a round card, any two 



-say a mouse and a trap, or cage. Through the 



>{ the card a string is passed, each end of which is 

 hdd! r and thumb. On twisting the 



i .ipidly round, the mouse and cage come successively 



to view; but 1 B rays reflected from the two 



silt-faces do not arrive at the same time on the retina, 



produced leads a person to suppose that the 



is running in and out of the cage. This arrange- 

 ment often at: .Id-able amusement to young 

 people ; and, of course, tho subjects may be varied to an 

 almost iinhmiii-il extent. 



The phantasmascope acts on similar principles ; but the 

 arrangement is very different. A circular piece of card- 

 board, of any diameter, is fixed on a handle by means of 

 a pin at i' on wluch it can freely turn round. 



On one side of the circle, figures, in different attitudes, 

 are pasted or painted, and over each a small slit is made. 

 On turning the card rapidly round, and looking through 

 the slits on a looking-glass placed in front, the reflection 

 of the figures, which seem to be in rapid motion and all 

 alive, will be seen. Amongst many of the illustrations 

 used a.e horses and men leaping gates, acrobats, (be. ; all 

 of which afford great amusement. The following engraving 

 (Fig. 67) illustrates the construction of this singular toy. 



Mr. Rose, of Glasgow, has invented a very interesting 

 instrument, which he has called the kalotrope. It consists 

 of a circular disc, on which are drawn, in deep lines, 

 various curved figures. Before this is placed a kind of 

 screen, perforated with divisions. Several of these are 

 furnished, and thus the effect is varied. The disc is 

 made to revolve rapidly by means of wheel-work ; whilst 

 the screen also revolves in front of the disc, either at a 



See ante, p. 49 



