176 



BECEEATIYE SCIENCE. 



To tlie topmost wheel I have fitted a 

 piece of oak, and upon this glued a circular 

 piece of stiff cardboard ; this forms my disc- 



Fia. 1. 



table to receive the coloured papers. Ver- 

 tically to this I have adapted a boxwood 

 spindle, with a screw formed at the bottom 



Fig, 2.— a, Stand ; B, Key ; C, Disc-table ; D, Black 

 pattern. 



end, and shouldered at the top to receive 

 patterns. The screw enters the oak through 

 the cardboard, and fixes the coloured papers 



while revolving. To the spindle of the lower- 

 most wheel I have fitted a pipe key, similar 

 to those used for French clocks. 



It must be borne in mind that one whole 

 turn of this key will produce upwards of 650 

 revolutions of the disc-table. Here we have, 

 then, very great power and mechanical lever- 

 age, and one also by which the speed can 

 easily be computed, a thousand revolutions 

 and upwards being obtainable per minute, 

 when required, or a very slow speed may be 

 maintained by the gentlest pressure of the 

 key, evolving effects hitherto unattainable ; 

 so that experiments may be tried, and their 

 formulae speed be described to friends at a 

 distance with a certainty of success, if re- 

 peated. The speed being continuous, a 

 coloured plane being fixed, the variation of 

 the colours may be observed, and disc after 

 disc tried, shifted, and others substituted, each 

 one being made to revolve at varying speeds, 

 producing many effects, as almost all my pat- 

 terns do; and the instrument being fixed in 

 one place, the eye may be brought to bear 

 upon it in its proper focal position. 



There is one other disadvantage I have 

 overcome — it is this : When a black disc is 



Fig. 3. 



revolving, the play of light upon it produces 

 a certain aberration, a hazy indistinctness. 



