XVIII. 



Supplement to Memoir XL of this Volume, on " The Numerical Relation between the 

 Atomic Weights, with some Thoughts on the Classification of the Chemical Elements."" 



SINCE the printing of the above memoir, the author has altered the details of his clas- 

 sification so far as regards the metallic elements, 1st, by transferring several members 

 of the Four Series to the Three Series ; 2d, by subdividing each of these series into 

 groups. The classification as thus altered is presented in the table accompanying the 

 memoir, and conforms to the principle of chemical series more closely than that given 

 in the table originally intended to accompany the memoir, and subsequently published 

 in the American Journal of Science and Arts, Second Series, Vol. XVII. p. 387. 

 The serial relations of the metallic elements may be traced, in the first place, in the 

 groups considered each as a whole, and, in the second place, in the members of any one 

 group by itself. From the limited amount of space assigned to this supplement, it will 

 not be possible to follow out these relations, but they will be suggested to any chemist 

 on inspecting the table. Most of the rarer metals have been omitted in it, not only 

 because their properties are generally very imperfectly known, but also because the 

 table was chiefly intended for teaching elementary chemistry. 



J. P. C. 



CAMBRIDGE, April 5th, 1856. 



ERRATA. 



Page 239, line IS, for mutantis, read mutatis. 

 " 241, " 14, " Eight Series, " Nine Series. 

 " 256, " 15, " Rhombic, " Hexagonal. 



