1818.] On the Kaleidoscope. 45l 



P.S. It will be necessary, after shaping the pumice stones, 

 and before excavating them, to bind each part round in several 

 places with iron or copper wires let into grooves, in order to 

 prevent their breaking asunder in that operation ; or afterwards, 

 by their unequal expansion and contraction, in heating and 



cooling. 



Article XV. 

 Dr. Brewster's Patent Kaleidoscope. From a Correspondent. 



From the great popularity of the kaleidoscope, attempts 

 have been made to discover the principle of the instrument, and 

 even the instrument itself in optical theorems, and in machines 

 long ago exploded and forgotten. The most plausible of these 

 attempts is that which supposes that the idea of the kaleido- 

 scope is taken from Bradley's gardening, which contains the 

 account of an instrument consisting of two plates of mirror glass 

 four inches high and five inches wide. These plates, connected 

 by a hinge, are placed upon a regular kind of drawing, and the 

 observer, looking in in front, sees the lines of the drawing multi- 

 plied so as to form garden plats of different forms. A few 

 instruments of this kind, made from Mr. Bradley's description, 

 have been in the possession of the public for more than 100 

 years ; and nobody either saw or heard of any beautiful effects 

 which they produced. The instrument is indeed incapable of pro- 

 ducing any effect approaching to the effects of the kaleidoscope ; 

 and among all the attempts to evade Dr. Brewster's patent, no 

 person has ever thought of making the instrument described by 

 Mr. Bradley. 



To those who are not capable of examining this subject scien- 

 tifically, it may be sufficient to subjoin the written attestations 

 of one of the most eminent natural philosophers of the present 

 day, who considers the instrument of Mr. Bradley as entirely 

 different in its principle and effects from the kaleidoscope 

 invented by Dr. Brewster. The following is an extract from the 

 opinion of Professor Playfair : 



" I have examined the kaleidoscope invented by Dr. Brew- 

 ster, and compared it with the description of an instrument 

 which it has been said to resemble, constructed by a person of 

 the name of Bradley. I have also compared its effects with a 

 theorem to which it may be thought to have some analogy 

 described by Wood in his Optics. R. M. 13 and 14.* From 



* Mr. Wood, of Cambridge, has also written a letter, in which he candidly states 

 " that the effects produced by the kaleidoscope were never in his contemplation " when 

 he drew up these two propositions, and that they " contain merely the mathematical 

 calculation of the number, and arrangement of the images." 



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