453 H'tslory of the Kaleidoscope. 



and Bradley's instrumertt, or such as Wood's or Harris's theories 

 ruighthave suggested, appear to me to have any real foundation; 

 but I can affirm, that neither in any of tl.e French, German, or 

 Italian authors, who, to my knowledge, have treated of optics, 

 nor in Professor Charles's justly celebrated and most complete 

 collection of optical instruments at Paris, have 1 read or seeu 

 any thing resembling your ingenious apparatus, which, from it* 

 numberless applications, and the pleasure it affords, and wiil 

 continue to afford, to millions of beholders of its matchless ef- 

 fect's, may be ranked among the most happy inventions science 

 ever presented to the lovers of rational enjoyment. 



"M. A. PiCTET, 

 " Professor of Nat. \'\\\\. in the 

 " To Br. Brewster." Academy ot Geneva. 



The propositions in Harris's Opticks relate, like Professor 

 Wood's, merely to the multiplication and circular anaugement 

 of the apertures or sectors formed by the inclined mirrors, and 

 to the progress of a ray of light reflected between two inclined or 

 parallel mirrors ; and no allusion whatever is made, in the pro- 

 positions themselves, to anv instrument. In the proposition re- 

 specting the multiplication of the sectors, the eye of the observer 

 is never once mentioned, and the proposition is true if the eve 

 has an infinite number of positions; whereas, in the kaleidoscope, 

 the eye can only have one position. In the other proposition. 

 (Prop. XVII.) respecting the progress of the rays, the eye and 

 the object are actually stated to be placed between thetejiectors; 

 and even if the eye had been placed without the reflectors, as iii 

 the kaleidoscope, the position assigned it, at a great distance 

 from the angular point, is a demonstration that Harris was en- 

 tirely ignorant of the positions of symmetry either for the object 

 or the eye, and could not have combined two reflectors so as to 

 form a kaleidoscope for producing beautiful or symmetrical forms. 

 The only practical part of Harris's propositions is the 5th and 

 r>th scholia to Prop. XVII. In the 5th scholium he proposes a 

 sort of catoptric box or cistula, known long before his time, com- 

 posed of four mirrors, arranged in a most unscientific manner, 

 and containing opaque objects between the specultims. '' What- 

 ever they are," s<ays he, when speaking of the objects, " the 

 upright figures between the speculums should be slender, and not 

 too many in number, otherwise they will too much obstruct thi 

 reflected rays from coming to the eye." This shows, in a most 

 decisive manner, that Harris knew nothing of the kaleidoscope, 

 and that he has not even improved the common catoptric'cistula, 

 which had been known long before. The principle of inversion, 

 and the positions of symmetry, were entirely unknown to him. 

 la ihc Gth scholium, ho speaks of rooms lined with looking- 

 glasses. 



