1863.] 453 



The replacement of hydrogen by a compound radical, aniline amyl- 

 aniline ; and water, alcohol, ether (according to Williamson's theory). 

 Of hydrogen by oxygen alcohol, acetic acid ; ether, acetic ether ; 

 and carvene, carvole, eugenic acid. Of hydrogen by peroxide of 

 nitrogen benzole, nitrobenzole, dinitrobenzole (in solution) ; gly- 

 cerine, nitroglycerine ; and amylic alcohol, nitrate of amyl. Of 

 hydrogen by chlorine benzole, chlorobenzole, terchlorobenzole ; 

 and the substitution of chlorine by bromine terchloride of phos- 

 phorus, terbromide of phosphorus ; chloroform, bromoform ; and 

 bichloride of chlor-ethylene, bibromide of chlor-ethylene, bibromide 

 of brom-ethylene. When hydrogen is replaced by some other body, 

 there is generally an increase of the actual refraction and dispersion ; 

 but this is due to the increased weight, hydrogen having a very low 

 actual, but a very high specific influence on the rays of light. In 

 each of the five instances of two substitution-products, as, for 

 instance, chlorobenzole and trichlorobenzole, the lower one always 

 retains in its optical properties an intermediate position between 

 the original substance and the higher product. 



These experiments on substitution sufficed to show, as the exa- 

 mination of isomeric bodies had done, that the special influence 

 exerted on the rays of light by the elements of a compound is 

 greatly dependent on the manner of their combination. 



The following is given as a generalization approximately, if not 

 absolutely true : Every liquid has a specific refractive energy com- 

 posed of the specific refractive energies of its component elements, 

 modified by the manner of combination, and which is unaffected by 

 change of temperature, and this refractive energy accompanies it 

 when mixed with other liquids. 



III. " On the Change of Form assumed by Wrought Iron and 

 other Metals when Heated and then Cooled by partial 

 immersion in Water." By Lieut. -Col. H. CLERK, R.A., 

 F.R.S. Received February 9, 1863. 



Origin of the Experiments. A short time ago, when about to 

 shoe a wheel with a hoop-tire, to which it was necessary to give a 

 bevel of about |-ths of an inch, one of the workmen employed sug- 

 gested that the bevel could be given by heating the tire red-hot and 



