450 ON BURNING GLASSES AND MIRRORS. [MEMOIR XXX. 



In Fig. 97, a a is the vessel filled with mercury ; I d, the 

 glass flask immersed in it, but having 

 at its upper part a small portion un- 

 covered, through which the converging 

 rays, <?, may come in. 



The power of a ray thus depending 

 on the degree of absorption exerted 

 upon it, I was led to inquire whether, 

 by admixture with other suitable sub- 

 stances in a solution undergoing de- 

 composition, the effect could be increased. Chlorine wa- 

 ter decomposes more rapidly as its yellow tint is deeper. 

 Four equal bulbs were therefore taken a, containing 

 chlorine water ; &, the same, deepened with chloride of 

 gold ; #, chlorine water, with commercial hydrochloric 

 acid of a yellow tint ; d, chlorine water, with tincture of 

 iodine. These were all exposed together to the sun. It 

 was at once obvious that a was giving off most oxygen, 

 and eventually it was found that b yielded a much 

 smaller quantity, and c and d none at all. The presence 

 of these bodies, therefore, exerted a prejudicial effect. 



A system of vibrating molecules will solicit an adja- 

 cent one to execute similar motions through the medium 

 of the intervening ether. A rise of temperature is due 

 to an increased rapidity or intensity of the oscillations 

 of the groups of vibrating molecules, but chemical de- 

 composition is due to the dislocation of their parts. It, 

 of course, by no means follows that when a compound 

 molecule is undergoing entire disruption, those in the 

 neighborhood should be compelled to pass into a similar 

 state. For the very reason that chemical decomposition 

 takes place is because the group that receives the pro- 

 voking ray cannot vibrate consentaneously with it; and 

 if that group cannot assume the motion in question, how 

 can it possibly transmit it to any other ? 



