172 PROCEEDINGS OF THE AMERICAN ACADEMY 



properties of the members of these triads, comparing them v/ith sim- 

 ilar analogies observed in Organic Chemistry, and drew, as is well 

 known, from these facts arguments to support the hypothesis of the 

 compound nature of many of the now received elements. Similar 

 views to those of Dumas have been advanced by other chemists. 



"The doctrine of triads is, however, as I hope to be able to show 

 in the present memoir, a partial view of this subject, since these triads 

 are only parts of series similar in all respects to the series of homo- 

 logues of Organic Chemistry, in which the differences between the 

 atomic weights of the members is a multiple of some whole number. 

 All the elements may be classified into six series, in each of which 

 this number is different, and may be said to characterize its series. 

 In the first it is 9, in the second 8, in the third 6, in the fourth 5, in the 

 fifth 4, and in the last 3." (See Table IV.) 



The paper speaks of the properties of the elements which are func- 

 tions of the atomic weights, and says that it does not seem bold the- 

 orizing to suppose that the atoms of the members of the same series 

 are formed of a common nucleus, to which has been added one or more 

 groups of atoms, or perhaps one or more single atoms, to which the 

 corresponding element has not been discovered. 



Referring to this subject in 1857,* M. Dumas said: "I have often 

 tried, as Mr. Josiah Cooke has on his part, to compare them, to com- 

 bine them, and to discuss them, with the hope of drawing some conclu- 

 sion from them with certainty, but I have been unable to draw from 

 them anything but doubt. The formula deduced from the above 

 simple progression " (a -j- n d) " would not account for the generation 

 of simple bodies, as Cooke had supposed, but organic radicles are not 

 always formed by addition, they are also produced by substitution, as 

 we see in the compound ammoniums." Dumas proposed to substitute 

 a formula like n a + n' d -\- n" d' ; a being the nucleus; d and d\ the 

 common differences ; and 7i, n', n", whole numbers. Table IV. shows 

 the series of Cooke and Dumas. 



Following in their footsteps, Professor Newlands extended their prin- 

 ciples to include newly discovered elements. Employing Cannizzaro's 

 atomic weights instead of those of the old system, and collating his own 

 results and all discovered up to 1864, he arranged the groups in hori- 

 zontal lines instead of vertical columns, and then discovered the " Law 

 of Octaves," as shown in Table IV. The coincidence of the ordinal 

 numbers led him, in 1865, to express the following opinion: "I will 



* Comptes Rendus, 1857, p. 709. 



