as connected wiih the Theory of Substitutions. 329 



plete mechanical explanation of the assumption of an active or 

 passive state. It may be remarked, that a very trivial modi- 

 fication of our admitted views of the relation between atoms 

 and their properties is all that is required to give a consistent 

 explanation of every one of these facts. Instead of regarding 

 the specific qualities of an atom as appertaining equally to the 

 whole of it in the aggregate, we have merely to assume that 

 there is a relation between its properties and its sides ; and 

 that any force which can make it change its position upon its 

 axis will throw it from the active to the passive state. But 

 this is nothing more than the well-known idea of the polarity 

 of atoms. 



Phcenomena of the Decompositio7i of Water by Chlorine in the 

 Rays of the Sun. 



From the various facts which might be employed, as offering 

 the means of establishing the allotropism of chlorine, I shall 

 select those which arise from an examination of the phaeno- 

 mena of the decomposition of an aqueous solution of chlorine 

 by the rays of the sun. 



For many years it has been known that an aqueous solu- 

 tion of chlorine undergoes decomposition by the aid of the 

 solar rays. Several of the most remarkable phaenomena con- 

 nected with this decomposition appear to have been over- 

 looked. Among such may be mentioned the singular fact, 

 that chlorine, which has thus been influenced by the sun, has 

 obtained the quality of effecting this "decomposition subse- 

 quently, to a measured extent, even in the dark. Not to an- 

 ticipate what I shall have to offer on this point, I shall now 

 proceed in the first place to establish the various facts con- 

 nected with the decomposition in question. 



Having provided a number of small glass vessels, consist- 

 ing of a bulb and neck, of the capacity of from 1*5 to 2'0 

 cubic inches, I filled them with a solution of chlorine in re- 

 cently boiled water, and inverted them in small glass bottles 

 containing the same solution, as shown in Plate IV. fig. 1. 

 With these bulbs the following experiments were made : — 



I. An aqueous solution of chlorine does not decompose in 

 the dark. 



One of the bulbs was shut up in a dark closet, and kept 

 there for a week, being examined from time to time. No de- 

 composition was perceptible, for no gas collected in the upper 

 part of the bulb. 



II. A solution of chlorine decomposes in the light. 



One of the bulbs was placed in a beam of the sun reflected 

 into the room by a heliostat. For sixteen minutes no change 



