of the Light emitted by Luminous Bodies. 7 



Since this method of measuring light first occurred 

 to me, I have made many improvements in the appa- 

 ratus employed in it ; and I have now brought the prin- 

 cipal instrument to such a degree of perfection that, 

 if I might, without being suspected of affectation, I 

 should dignify it with a name, and call it a photometer. 

 I have likewise made a considerable number of ex- 

 periments, with a view to determining the relative 

 quantities of light produced by lamps and candles of 

 different kinds, and the relative expense of lighting 

 rooms in different ways ; but, before I proceed to give 

 an account of them, it will be necessary to describe 

 very particularly the alterations I have found it expe- 

 dient to make in the instruments employed in making 

 them. 



And, in the first place, the shadows, instead of being 

 thrown upon a paper spread out upon the wainscot or 

 side of the room, are now projected upon the inside 

 of the back part of a wooden box, 7^ inches wide, 

 io|- inches long, and 3^ inches deep, in the clear, open 

 in front to receive the light, and painted black on the 

 inside, in every part except the back, upon which the 

 white paper is fastened which receives the shadows. 

 To the under part of the box is fitted a ball and 

 socket, by which it is attached to a stand which sup- 

 ports it ; and the top or lid of it is fitted with hinges, 

 in order that the box may be laid quite open as often 

 as it is necessary to alter any part of the machinery it 

 contains. The front of the box is likewise furnished 

 with a falling lid or door, movable upon hinges, by 

 which the box is closed in front when it is not in 

 actual use. 



Finding it very inconvenient to compare two shad- 



