MEMOIR XXX.] ON BURNING GLASSES AND MIRRORS. 445 



idly, the water was depressed in the bulb by the steam 

 and bromine vapor which occupied the upper part, the 

 bulb being placed uppermost, and the tube dipping into 

 a phial which served as a reservoir. After the exposure 

 had continued for two hours and a half, the matrass was 

 removed from the lens and suffered to cool. There re- 

 mained uncondensed a little bubble, measuring about yJ-Q 

 of a cubic inch ; but this was probably nothing more 

 than the atmospheric air which had found access to the 

 water, for on submitting the same specimen to another 

 exposure for three hours, after the gas had been decanted 

 from it, a little bubble, the diameter of which was esti- 

 mated at one fiftieth of an inch, was all that could be 

 procured. 



In Fig. 93, a is the flask containing the bromine water ; 

 &, a phial serving as a reservoir. It is half filled 

 w 7 ith the same water. 



In like manner I endeavored to decompose wa- 

 ter by iodine, and with the same negative result, 

 even when the exposure to the focal point lasted 

 four hours. When proper care had been taken 



to remove from the solution all traces of air, no Fig. 93. 

 gas was evolved. 



To reduce the heating effect of the lens, and allow the 

 more refrangible rays alone to act, there was interposed 

 between the lens and its focus a stratum of a solution of 

 sulphate of copper and ammonia one third of an inch 

 thick, included between two flat plates of glass, suitably 

 arranged and carried along with the other parts by the 

 movement of the clock. The cone of solar rays now 

 passed through this absorbent medium (Fig. 94). 



In Fig. 94, #, 1) is the flask and reservoir, but the con- 

 verging rays pass through an absorbent trough, c c, 

 shown in front view at d, e being the circular cell con- 

 taining the blue solution. 



