Curiosities of Science. 43 



HOW TO MAKE A MAGIC MIRROR. 



Draw a figure with weak gum-water upon the surface of a 

 convex mirror. The thin film of gum thus deposited on the 

 outline or details of the figure will not be visible in dispersed 

 daylight ; but when made to reflect the rays of the sun, or those 

 of a divergent pencil, will be beautifully displayed by the lines 

 and tints occasioned by the diffraction of light, or the inter- 

 ference of the rays passing through the film with those which 

 pass by it. 



SIR DAVID BREWSTER'S KALEIDOSCOPE. 



The idea of this instrument, constructed for the purpose of 

 creating and exhibiting a variety of beautiful and perfectly 

 symmetrical forms, first occurred to Sir David Brewster in 1814, 

 when he was engaged in experiments on the polarisation of 

 light by successive reflections between plates of glass. The 

 reflectors were in some instances inclined to each other ; and 

 he had occasion to remark the circular arrangement of the 

 images of a candle round a centre, or the multiplication of the 

 sectors formed by the extremities of the glass plates. In repeat- 

 ing at a subsequent period the experiments of M. Biot on the 

 action of fluids upon light, Sir David Brewster placed the fluids 

 in a trough, formed by two plates of glass cemented together at 

 an angle ; and the eye being necessarily placed at one end, some 

 of the cement, which had been pressed through between the 

 plates, appeared to be arranged into a regular figure. The re- 

 markable symmetry which it presented led to Dr. Brewster's 

 investigation of the cause of this phenomenon ; and in so doing 

 he discovered the leading principles of the Kaleidoscope. 



By the advice of his friends, Dr. Brewster took out a patent 

 for his invention ; in the specification of which he describes the 

 kaleidoscope in two different forms. The instrument, however, 

 having been shown to several opticians in London, became 

 known before he could avail himself of his patent ; and being 

 simple in principle, it was at once largely manufactured. It is 

 calculated that not less than 200,000 kaleidoscopes were sold 

 in three months in London and Paris ; though out of this num- 

 ber, Dr. Brewster says, not perhaps 1000 were constructed upon 

 scientific principles, or were capable of giving any thing like a 

 correct idea of the power of his kaleidoscope. 



THE KALEIDOSCOPE THOUGHT TO BE ANTICIPATED. 



In the seventh edition of a work on gardening and plant- 

 ing, published in 1739, by Richard Bradley, F.K.S., late Pro- 

 fessor of Botany in the University of Cambridge, we find the 

 following details of an invention, u by which the best de- 



