516 Notices of Memoirs — Rev. E. Sill — Density of Meteorites. 



Section E. — Geography. 

 J. Y. Buchanan. — Oceanic Islands and Shoals. 



Gen. Sir B. Lefroy. — On the Depth of the Permanently Frozen 

 Stratum of Soil in British North America. 



Section G. — Mechanical Science. 

 W. Smith. — The Movement of Sand in Aberdeen Bay. 



Section H. 

 Thomas Wilson. — A New Man of Mentone. 

 W. PengelJy — Happaway Cavern, Torquay. 

 Dr. J. G. Garson. — The Human Kemains found in Happaway Cavern, 



Torquay. 

 Dr. B. Munro. — The Archeeological Importance of Ancient British 



Lake-Dwellings and their Eelation to analogous Eemains in 



Europe. 



Papers read before Section C (Geology). 

 n. — On the Average Density of Meteorites compared with 



THAT OF the EaRTH. 

 By the Eev. E. Hill, M.A., St. John's College, Cambridge. 



THE mean density of the earth, though not yet exactly deter- 

 mined, is certainly about twice the average density of the 

 rocks which compose its superficial crust. One conjecture which 

 very naturally follows from this fact is that the constituents of its 

 interior may essentially differ from the constituents of that crust. 

 Professor Judd in his treatise on Volcanoes has alluded to this, and 

 brings forward in addition the argument that materials are occasion- 

 ally brought from below to the surface which resemble the materials 

 of meteorites ; bodies which generally have a high specific gravity 

 and sometimes consist entirely of iron.^ The thought has occurred 

 to me that it would be interesting to ascertain the average specific 

 gravity of meteorites, in order to estimate what would be the density 

 of a body formed by the aggregation of a multitude of such objects. 



To conduct such an investigation properly would involve enormous 

 labour of research, and I have contented myself by using the 

 materials furnished by Dr. Walter Flight's most valuable "Chapters 

 on Meteorites," published in the Geological Magazine, during the 

 years 1875, 1882, and 1883. From those chapters I have obtained 

 the specific gravities of sixty -five difierent meteoric masses there 

 described. The mean of these values, found by addition and division 

 by 65, gives as result 4-84. 



This method of obtaining the mean will be correct, if the various 

 sizes were equally distributed through each of the different specific 

 gravities. This would be rather a rash assumption, and it may 

 seem fairer to bring into account the difi"erent masses of the specimens. 

 From Dr. Flight's papers, with some other materials, I have found 

 fifty-seven cases in which both weight and specific gravity are 

 recorded. Taking the sum of the weights, the sum of the corre- 

 spcmding volumes, and dividing, we obtain as final result a specific 

 gravity of 5-71. 



1 "Volcanoes," p. 320. 



