of the Light emitted by Luminous Bodies. 43 



periment, are placed at different distances from the 

 field of the photometer, the shadows of the two equal 

 cylinders, unassisted by their projecting wings, will of 

 course be of unequal widths. To bring their widths 

 to be equal was the sole object of the contrivance we 

 have been describing. 



/, m, n (Fig. i, Plate I.), are the three strong feet 

 which support the photometer, and also a round table 

 on which one end of each of the long narrow tables 

 rests that support the sliding carriages which carry the 

 lights. In each of these feet there is a screw (repre- 

 sented more distinctly in the Fig. 2, Plate 11.) by 

 means of which the stand or pillar which supports the 

 photometer may be brought into a position exactly 

 vertical. 



A ground plan of a part of one of the long and 

 narrow tables (that on the right hand) is represented 

 in this figure ; and a part also of one of the carriages 

 which carry the lights is seen at 0^ p, q^ r. The top of 

 the pulley is also seen, and the line which passing 

 over it draws the carriage on which the light stands. 

 The place occupied by one end (that next to the pho- 

 tometer) of the other long table is represented by the 

 dotted lines /, u, w, x. The place of the strong pin 

 which, passing through a hole made to receive it, near 

 the end of the table, is represented (in a ground plan) 

 at s. These pins are shown very distinctly at s, s, in 

 the Fig. 2, Plate II. 



I, 2, 3, Figs. I and 2, are three strong braces which 

 assist in supporting the pillar, on the top of which the 

 photometer is placed. 



T in the Figs, i and 2 is a strong circular table 

 on which one end of each of the long narrow tables is 



