108 E. Hodgkinson, Esq., on the 



tion to this law, though the author believes that the excep- 

 tion is only apparent, and that further observations will 

 enable us to refer the reproductive organization of this 

 zoophite to the same type with that of Cordylophora and the 

 marine Ilydroida. The author has satisfied himself that the 

 ova-like bodies contained in the capsules of Cordylophora 

 are true ova, and not gemmce ; he has demonstrated in them 

 a distinct germinal vesicle, and has witnessed the pheno- 

 menon of yelk-cleavage ; and the paper details the develop- 

 ment of the embryo to the period of its escape from the cap- 

 sule in the form of a free -swimming ciliated animacule, and 

 traces its subsequent progress into the condition of the adult 

 zoophyte. — {Proceedings of the Royal Society, London, 1853). 



On the Elasticity of Stone and Crystalline Bodies. 

 By E. Hodgkinson, Esq.* 



It is generally assumed by writers on the strength of ma- 

 terials, that the elasticity of bodies is perfect, so long as the 

 material is not strained beyond a certain degree. But from 

 the experiments I. made several years ago, at the instance of 

 the British Association, on the strength of Hot and Cold 

 Blast-iron (vol. vi.), I was led to conclude that the assump- 

 tion was very incorrect, as applied to cast-iron at least ; and 

 further experiments rendered it probable that it was only an 

 approximation in any. Among the bodies of most value in 

 the arts, cast-iron holds an important place ; and I found 

 that bars of that metal, when bent with forces, however small, 

 never regained their first form, after the force was removed ; 

 and this defect of its elasticity took place whether the cast- 

 iron was strained by tension, compression, or transverse 

 flexure. I subsequently found that in the first two strains 

 (by tension and compression), the straining force might be 

 well represented by a function composed of the first and se- 

 cond powers of the change of length produced, — thus, 

 w = ae — be 2 

 w = a'c — b'c 2 



* Read before the Meeting of the British Association for the Advancement 

 of Science at Hull. 



