Roijal Socieli/. S85 



crystallization. Thus at p. 356, muriate of baiytes is said to crystal- 

 lize in four, six, or eight-sided tables, without any reference to its 

 primary or secondary forms ; and the form of a six-sided prism, 

 bounded by pyramids with six sides, in which sulphate of potash is 

 said to crystallize, is not merely a secondary one, but a made. In 

 p. 358, line 7, we have 108 parts or one atom of water, instead as 

 we presume, 12 atoms ; and in the next page, line 14, calcium oc- 

 curs instead as we suppose, of strontium; and in p. 262, chloride of 

 calcium, is substituted for chloride of lime. 



There are some statements respecting the oxides and salts of man- 

 ganese which require careful revision; and although, as we have had 

 frequent occasion to show. Dr. Turner's work bears evident marks of 

 occasional haste, it v.'ill in general be found a safe guide for the 

 student. We would advise the author, however, to give more rules 

 for conducting processes ; and towards the latter part of the work 

 especially, the compositions of bodies are too frequently omitted. 

 And we cannot help observing, that the graphic illustrations are not 

 sufficiently numerous, and are altogether unworthy of the work. 



LXXVI. Proceedings of' Learned Societies. 



ROYAI- SOCIETY. 

 March 22. — T^HE reading of iMr. Whewell's paper On experi- 

 J>- ments made at Dolcoath mine in Cornwall, to de- 

 termine the density of the earth, was concluded ; and Professor 

 Airy's Appendix to it also read. 



» The experiments described in this paper were made with two in- 

 variable pendulums, one swung at the surface of the ground at Dol- 

 coath, the other at the depth of 1220 feet in the mine. The pro- 

 secution of them beyond a certain point, and their complete verifi- 

 cation by a second exchange of the pendulums between the two sta- 

 tions, was rendered impossible by the accidental destruction of one 

 of the pendulums. Tlieir result, however, down to this point, gives 

 8"-23 per day, for the sum of the variations or double variation, of 

 each of the pendulums, observed above and below. And Mr. Whe- 

 well considers that this result is the inevitable consequence of tlie 

 observations ; although very much greater than could have been 

 anticipated, from any opinion hitherto entertained of the earth's in- 

 ternal structure and density. In reasoning on this result the author 

 concludes, that it would require a mean density of the earth equal 

 to 773 times that of the superficial stratum, or about 20 times that 

 of water, to produce tlie difference of 8" 23 observed : tliat had it 

 been only G", still a density of 13 times that of water would be re- 

 quired ; but that the usual estimate resulting from the calculations 

 of Hutton and Zach, would reduce the difference to 2"-46, a quan- 

 tity too distant from that observed, to be attributable to any error 

 of their observations. Neither can this difl'erencc be attributed to 

 local attractions, or to the removal of the matter in the mine ; but 



considering the uncertainty, under which, from the accident above 



mentioned, tiie results labour, Mr. Whewell regards any exact cal- 



Nevo Series. Vol. 1. No. 5. May 1827. 3 D culations 



