538 Dr. Herschel's Experiments on the solar, and 



The bricks are piled up, as represented in Fig. 3. The stove, 

 Fig. 2, being prepared, bring the stand, and brick-work, Fig. 3^ 

 close to it; and set also the two spare bricks, which lie on the 

 stand, upon the front of the stove, that no heat may pass from 

 the top of it to the brick inclosure ; then put the box, Fig. 1, 

 into the brick-work, close up to the stove, and begin the expe- 

 riment. The ash-hole should also be covered with a brick. 



Plate XXVI. Fig. 1, represents the Photometer. The hole 

 at A, is for the observer to look through, that he may have a 

 fixed station. The vanes F and G are moveable. By pulling 

 the string at H, G will be brought nearer the lamp placed at 

 K ; and, by drawing the same string at I, it will be removed 

 towards the vane F ; which latter may be fixed at any distance 

 most convenient for the experiment. 



Fig. 2 and 3, shew the mechanism of the adjustable vane 2, 

 and moveable one 3. There are, however, hooks on fig. 2, which 

 will occasionally receive the strings from the hooks on fig. 3, 

 when a motion of the left vane, instead of the right, is required. 



Fig. 4, contains two limiting holes B, C ; over one of which, 

 C, a glass may be laid. This piece is to be buttoned on the rab- 

 bet of the screen, at D E, fig. 1. When liquids are to be tried, 

 the second piece of fig. 4, which contains a bracket for support- 

 ing the transmitting tube, is to be fastened on D E, fig. 1, instead 

 of the former plate. 



Fig. 5, gives a view of the lamp and its sliding door, with the 

 spout L, which, when the lamp is placed at K, fig. 1, conveys 

 the light to the vanes F and G, without permitting it to be 

 scattered on the long board. 



