APPENDIX, 



No. I. 



I HERE briefly describe the principal works known to 

 me which bear on the subject of the present volume. 



POINSOT (L.) Sur la composition des moments et la composition des 

 aires (1804). Paris Journal de 1'Ecole Polytechnique ; t. vi. 

 13 cah., pp. 182-205 (1806). 



In this paper the author of the conception of the couple, and 

 of the laws of composition of couples, has demonstrated the 

 important theorem that any system of forces applied to a rigid 

 body can be reduced to a single force, and a couple in a plane perpen- 

 dicular to the force. 



CHASLES (M.) Note sur les proprietes generales du systeme de deux 

 corps semblables entfeux et places d'une maniere quelconque 

 dans Vespace; et sur le deplacement fini ou infiniment petit 

 d?un corps solide libre. Bulletin des Sciences Mathe*ma- 

 tiques, par Ferussac. Vol. xiv., pp. 321-326 (Paris, 

 1830). 



The author shows that there always exists one straight line, 

 about which it is only necessary to rotate one of the bodies 

 to place it similarly to the other. Whence (p. 324) he is led to 

 the following fundamental theorem : 



Eon peut ioujours transporter un corps solide libre d'une position 

 dans une autre position quelconque, determime par le mouvement con- 

 tinu d'une vis a laquelle ce corps serait fixk invariablement . 



N 



