1 88 Management of Light in Illumination. 



less expensive than that I formerly recommended, I 

 have taken pains to describe it very particularly; and, 

 to save others the trouble which I have had in making 

 the calculations which were necessary in order to form 

 the graduated scale of the instrument, I shall here give 

 a table in which the measure of each of those divisions 

 will be expressed in feet and inches : 



By the help of this table the scale may be graduated 

 without any difficulty, and the whole of the apparatus 

 constructed and completely finished by any cabinet- 

 maker or joiner of common talents. 



As the improvement and simplification of the instru- 

 ments which are necessary in scientific investigations 

 have a powerful tendency to facilitate useful discov- 

 eries, too much pains cannot be taken in describing 



