374 Royal Society : — 



"With regard to these facts he observes that no difference of opinion 

 can arise, unless the sources from which they have been derived are 

 incorrect ; but that differences of opinion may be entertained rela- 

 tive to the interpretation of them. 



The interpretation to which the author inclines is, that the near 

 ao'reement in angle between two corresponding faces is not simply 

 accidental, but that it is the effect of some natural relation not 

 hitherto noticed, among all the crystals in each respective system ; 

 and hence, that where the angles between particular faces nearly 

 agree, there ought to be a corresponding agreement in the forms of 

 their symbols. 



With this view of the subject in his mind, it occurred to the 

 author that there might be a similar agreement among the whole of 

 the elementary angles in each system, and an examination of the 

 crystals in the pyramidal and rhombohedral systems to ascertain 

 how far this conjecture might be well-founded, has shown that a 

 geometrical isomorphism does exist throughout each of these systems, 

 and that similar relations may therefore be imagined to exist in the 

 other systems. 



The author has also suggested that the oblique and anorthic 

 systems are only hemihedral and tetartohedral varieties of prismatic 

 crystals. 



"On some Compounds of Ethylene." By H. L. Buff. 



Among the hydrocarbons which are capable of replacing hydro- 

 gen, the radicals of the general formula C„H(„+i), i. e. the homo- 

 loo'ues of ethyle, are best examined. There is another class of hydro- 

 carbons which may be represented by the general formula C„ H(n-i). 

 The only well-known term of this series is the radical allyle, Cg H5, to 

 which the attention of chemists has been especially called of late by 

 the researches of Messrs. Hofmanu and Cahours on allylic alcohol. 

 These researches have established the most perfect parallehsm be- 

 tween the two classes of radicals and their derivatives. Both the 

 radicals C«H(«+i) and C„ H(„_i) are monatomic, i.e. molecules capable 

 of replacing 1 equiv. of hydrogen. 



These two classes stand in the closest relation to each other, and 

 it is by no means improbable that one class may pass over into the 

 other, for instance, that the radical propyle Cg H7, or a propyle-com- 

 pound, may be converted into allyle or an allyle-compound. 



There exist a third series of hydrocarbons, which, again, both by 

 composition and origin, are closely allied to the former two. They 

 are represented by the general formula C„H„; and methylene, CgHj, 

 ethylene, C4H4, and propylene, CgHg, are well-known terms belonging 

 to this series. These hydrocarbons are also radicals ; they differ, 

 however, in their nature essentially from those of the former groups, 

 inasmuch as they are hiatomic molecules, i. e, molecules capable of 

 replacing 2 equivs. of hydrogen. 



There exist parallel with these three series of radicals which form 

 alcohols, three other groups of radicals, which in acids play exactly 

 the same part that in the alcohols is assigned to the hydrocarbons. 





