DECOMPOSITION BY LIGHT. 107 



The remark already made, as to the bearing of the 

 decomposition of nitrite of amyl by light on the ques- 

 tion of molecular absorption, applies here also; for were 

 the absorption the work of the molecule as a whole, 

 the iodine would not be dislodged from the allyl with 

 which it is combined. The non-synchronism of iodine 

 with the waves of obscure heat is illustrated by its mar- 

 vellous transparency to such heat. May not its syn- 

 chronism with the waves of light in the present instance 

 be the cause of its divorce from the allyl? 



Iodide of Isopropyl. The action of light upon- the 

 \apour of this liquid is, at first, more languid than upon 

 iodide of allyl; indeed many beautiful reactions may 

 be overlooked, in consequence of this languor at the 

 commencement. After some minutes' exposure, how- 

 ever, clouds begin to form, which grow in density and 

 in beauty as the light continues to act. In every ex- 

 periment hitherto made with this substance the column 

 of cloud filling the experimental tube, was divided into 

 two distinct parts near the middle of the tube. In one 

 experiment a globe of cloud formed at the centre, from 

 which, right and left, issued an axis uniting the globe 

 with two adjacent cylinders. Both globe and cylinders 

 were animated by a common motion of rotation. As 

 the action continued, paroxysms of motion were mani- 

 fested; the various parts of the clouds would rush 

 through each other with sudden violence. During 

 these motions beautiful and grotesque cloud-forms were 

 developed. At some places the nebulous mass would 

 become ribbed so as to resemble the graining of wood; a 

 longitudinal motion would at times generate in it a 

 series of curved transverse bands, the retarding influ- 

 ence of the sides of the tube causing an appearance re- 

 sembling, on a small scale, the dirt-bands of the Mer de 

 Glace. In the anterior portion of the tube those sudden 



