1818.] History of Dr. Brewster's Kaleidoscope. 63 



3. In Bradley's instrument, 3. In the kaleidoscope, the 

 from the erroneous position of eye is placed so that the uni- 

 the eye, there is a great inequa- formity of light is a maximum, 

 lity of light in the sectors, and and the last sectors are dis- 

 the last sectors are scarcely tinctly visible. 



visible. 



4. In Bradley's instrument, 4. In the kaleidoscope, all 

 the figure consists of elliptical, the sectors are equal, and 

 and consequently unequal sec- compose a perfect circle, and 

 tors. the picture is perfectly sym- 

 metrical. 



5. In Bradley's instrument, 5. In the kaleidoscope, the 

 the unequal sectors do not unite, equal sectors all unite into a 

 but are all separated from one complete and perfectly symme- 

 another by a space equal to the trical figure. 



thickness of the mirror glass. 



6*. In Bradley's instrument, 6. In the kaleidoscope, the 

 the images reflected from the secondary reflections are en- 

 first surface interfere with those tirely removed, and therefore 

 reflected from the second, and no confusion takes place, 

 produce a confusion and over- 

 lapping of images entirely in- 

 consistent with symmetry. 



7. In Bradley's instrument, 7. In the kaleidoscope, the 

 the defects in the junction of eye is placed so that these 

 the plates are all rendered visi- defects of junction are invi- 

 ble by the erroneous position of sible. 

 the eye. 



The reader will observe, that in this comparison the two 

 instruments are supposed to be applied to geometric lines upon 

 paper, and that this was the only purpose to which Bradley ever 

 thought of applying his mirrors ; yet the kaleidoscope is in every 

 respect a superior instrument, even for that inferior purpose, and 

 gives true symmetrical forms, which the other instrument is 

 incapable of doing. 



In the comparison which has now been made, we have 

 degraded the kaleidoscope by contrasting its effects with those 

 which Bradley's instrument is capable of producing, for these 

 effects are not worth the looking at. When we attempt to 

 employ Bradley's instrument to produce the effects which have 

 been so much admired in the kaleidoscope, namely, to produce 

 beautiful forms from transparent or opaque-coloured objects 

 contained in a cell, and at the end of the reflectors it fails so 

 entirely that no person has succeeded in the attempt. It is 

 indeed quite impossible to produce by it the beautiful and 

 symmetrical forms which the kaleidoscope displays. Had this 

 been possible, Dr. Brewster's patent might have been invaded 

 with impunity by every person who chose to manufacture Brad- 



