,501 
M. Dumas on the La^ of Substitutions, 
Pratt’s Philidor. Lond. 1825, 8vo. (I pass over many Ma- 
gazine articles, and brief notices of the knight-problem, 
in numerous works on chess ; as well in various collections 
of a general character, as Guyot’s Recreations, &c.). 
Ciccolini. Del Cavallo degli Scacchi. Paris, 1836, 4to, 
pp. 70, and 20 large plates. (This volume treats not only 
on the problem of the knight’s move over the common 
chess-board of 64? squares ; but also on the larger field of 
100 squares; as well as the circular board of 64?.). 
La Corso del Cavallo per tutti gli Scacchi della Scacchiere. 
Bologna, 1766, 4to. 
Collini. Solution du probleme du Cavalier, &c. Manheim, 
1773, 8vo. pp. 62. 
Essai sur les problemes de situation. Rouen, 1783, 8vo. 
pp. 74?. 
Der Roesselsprung, &c. bei Eduard Billig. 1831, 24mo. 
pp. 64-. 
Warnsdorf, H. C. von. Des Roesselsprunges, &c. Schmal- 
kalden, 1823. 4to, pp. 68. 
Lettre adressee aux auteurs du Journal Encyclopedique sur 
un Probleme de I’Echiquier. Prague, 1773. 
Dollinger, 24? verschiedene Arten den Springer, 8cc, Wien, 
1806, 8vo. 
Netto das Schachspiel : — And numerous other German writers. 
LXXVI. Memoir on the Law of Substitutions^ and the Theory 
of Mechanical Types, By M. Dumas. 
[Continued from p. 447.] 
Mechanical Types, 
A FTER having verified in a manner which satisfied my own 
conviction, the existence of certain chemical types, I tried 
the general application of this theory of types to all the 
known series produced by substitution, and last year at the 
School of Medicine I made this system of ideas the basis 
of iny lectures. 
But always constant to the experimental progress of the 
science, and wishing never to swerve from it, I asked myself 
whether it was necessary to class together bodies having the 
same formula, produced by substitution, but essentially dif- 
ferent in their most prominent chemical properties ? 
I said, the bodies produced by substitution are divided into 
two different classes: some evidently belong to the same 
