131 



ellipse is much more elongated, even at great angles of inci- 

 dence. 



" 4thly, Two reflections from silver increase the polarizing effect 

 of metals. This fact has its counterpart in light. Two reflections 

 likewise produce an increased tendency to circular polarization 

 when the plane of reflection is inclined 45° to that of primitive 

 polarization. This effect increases with the obliquity of incidence 

 up to considerable angles. 



" These observations have been verified in the case of heat from 

 various sources, obscure as well as luminous." 



Monday Uh April. 

 Dk hope, Vice-President, in the Chair. 

 The following Donations were presented : 

 Transactions of the Geological Society of London (second series). 



Vol. iv. Part 1. 

 Proceedings of the Geological Society of London, Nos. 42, 43 and 



44. — By the Society. 

 Bulletin de la Societe Geologique de France. Tome vii. Feuilles 



1_2. — By the Society. 

 Tables des Positions Geographiques des Principaux Lieux du Globe; 



par M. Daussy. 

 Second Memoire sur les Marees des Cotes de France; par M. 

 Daussy. — By the. Author. 



The following Communications were read : 

 1. On Paracyanogen and its Compounds. By James F. W. 



Johnston, Esq. 

 In this paper the author shewed that pure dry bicyanide of mer- 

 cury, when heated in close vessels, gave off mercury and pure cya- 

 nogen only, yet that there remained always in the retort a portion 

 of a black substance of variable density and lustre. He then pro- 

 ceeded, by a new series of analyses, to confirm what he had stated 

 several years ago, that this black substance is identical in composi- 

 tion with cyanogen, being, like that gas, represented by the formula 

 NC . To this solution he gives the name of Paracyanogen. He 

 then stated that the black substance deposited in strong prussic 

 acid, by a solution of cyanogen in water, in alcohol, in solution of 



