IO4 Management of Light in Illumination. 



which came into very general use in Bavaria; but, as 

 both these are inferior in many respects to the lamps 

 I shall recommend in this Essay, I have not thought 

 that it would be useful to publish any description of 

 them. 



As it is a duty incumbent on those who publicly 

 recommend new improvements, not only to show their 

 utility in the clearest manner, but also to explain the 

 principles on which they are grounded, in treating of 

 illumination, I must first investigate the principles on 

 which that art must be established, and must then 

 point out the particular objects which must be had in 

 view in all attempts to improve the instruments em- 

 ployed in the practice of it. 



As artificial light is employed to illuminate sur- 

 rounding objects to the end that they may be easily 

 and distinctly seen, it is necessary to inquire what cir- 

 cumstances are favourable to distinct vision, and also 

 what circumstances are unfavourable to it. 



If the facility with which objects are distinguished 

 by the eye depended solely on the intensity of the 

 light by which they are illuminated, this particular 

 inquiry would be superfluous; but that is very far 

 indeed from being the case. 



We can see objects, and even very distinctly, when 

 they are illuminated by light of very different degrees 

 of intensity. 



It is a well-known fact that a book may be read at 

 night by the light of the full moon, when the air is 

 very clear ; and everybody knows that it may be read 

 when illuminated by the direct rays of a bright merid- 

 ian sun. The differences of the intensities of the light 

 in these two cases is truly astonishing: the intensity of 



