Management of Light iii Illumination. 173 



inches in diameter is four times greater than it would 

 be if the diameter of the globe were eight inches. Now, 

 as the quantity of light emitted will be the same in both 

 cases, surrounding bodies will be illuminated as much 

 in one case as in the other; but the illumination will 

 be most mild, equal, and agreeable when the larger 

 globe is used, and the eyes will be in much less danger 

 of being fatigued and injured. 



As the system of illumination which I have recom- 

 mended is founded entirely on the supposition that 

 light may be dispersed without being destroyed, I feel 

 it to be necessary to establish that fundamental prin- 

 ciple in such a manner as to exclude all doubt. I shall 

 therefore go over the ground again, and shall endeavour 

 to elucidate the subject in the clearest manner. 



The experiment which was made with two burning 

 wax candles placed in two glass jars, the one of ground 

 glass and the other of transparent glass, certainly 

 proved that very little light is lost in passing through 

 ground glass, or at least not much more than is lost 

 in passing through the same kind of glass when it is 

 transparent ; but there are other experiments by which 

 it may be made quite evident that screens of ground 

 glass, and of other substances, may, under certain cir- 

 cumstances, be so arranged as even to augment the 

 intensity of the illumination of surrounding objects. 



If on a dark night a burning candle, fixed in the 

 centre of a cylindrical screen of ground glass, 6 inches 

 in diameter and 6 inches in height, be placed on a 

 small stand in the open air, it will illuminate surround- 

 ing objects as much as the same candle would be able 

 to illuminate them if the screen were made of transpar- 

 ent glass. 



