i8o Management of LigJit in Illumination, 



There is a very obvious improvement that may 

 easily be made in the construction of the domes of 

 table illuminators, which must occur to everybody. As 

 these domes are not very large, they may be made of 

 blown glass, and after their surface shall have been 

 made rough by grinding they may be ornamented so 

 as to make them very beautiful, when lighted, by paint- 

 ing them on the inside in various ways with white 

 paint. This paint must be mixed up with oil of pop- 

 pies or with white copal varnish, in order that the 

 figures represented may at night appear through the 

 glass like shades, and without colour. By day they will 

 not be seen. 



Glass domes and vases for illuminators might be 

 very elegantly ornamented by etchings made with the 

 fluoric acid ; and it is very probable that the surface of 

 the glass might be made rough by means of that acid, 

 and perhaps at a less expense than when its polish is 

 taken off by grinding it with emery. 



But I am afraid of being tiresome by dwelling so 

 long on these details. 



CHAPTER IV. 



Description of a very simple Contrivance for measur- 

 ing the Intensity of the Light emitted by Lamps 

 and Candles and other luminous Bodies. — Means 

 of estimating of the Light lost in passing through 

 Screens. — Experiments for ascertaining what Sub- 

 stances are most proper for co7istructing luminous 

 Screens for Lamps and Candles. 



