xxxvn 



lucid and graphic considerations, by means of which a great geometer, 

 employing the ingenious doctrine of couples in dynamics, has un- 

 folded all the geometric and dynamic properties of a heavy body in 

 motion. . . .With the sole aid of geometric reasoning, M. Poinsot 

 renders palpable, and depicts all the circumstances of the motion of 

 a solid. 



The titles and dates of M. Poinsot's principal works are as fol- 

 lows : " Sur les polygones et les polyedres," Journal de 1'Ecole 

 Polytechnique, 1 809 ; " Memoire sur 1'application de 1' Algebre a la 

 theorie des nombres et a la recherche des racines primitives," Journal 

 de 1'Ecole Polytechnique, 1320 ; ' Elements de Statique, suivis de 

 quatre Memoires";' " Sur la composition des moments et des aires dans 

 la mecanique" (from the Journal de 1'Ecole Polytechnique, 1804); 

 ' Sur le plan invariable du systeme du Monde ;' ' Theorie generate 

 de I'equilibre et du mouvement des systemes ;' ' Theorie nouvelle de 

 la rotation des cords,' a classical work, in which M. Poinsot first 

 propounded his beautiful theory of couples, and of which the 9th 

 edition appeared in 1848; 'Recherches sur T Analyse des sections 

 angulaires,' 1825; 'Reflexions sur les principes fondamentaux de 

 la theorie- des nombres,' 1845 ; 'Theorie nouvelle de la rotation des 

 corps,' 1851; 'Theorie des cones circulaires roulants,' 1853; 

 ' Sur la percussion des corps,' 1 85 7 ; ' Precession des Equinoxes,' 

 1857 ; 'Note sur la theorie des polyedres,' 1858. 



HEINRICH RATHKE was the son of a ship-carpenter of Dantzic, 

 and was born in that town on the 25th of August, 1793. Being 

 destined for the medical profession, he studied with that view in 

 Gottingen and in Berlin, and in 1818 he commenced practice in his 

 native city. While at Gottingen, however, he had acquired under 

 the mastership of Blumenbach a decided taste for zootomical and zoo- 

 logical pursuits, and had, even in his student years, undertaken 

 original researches in these branches of science. Accordingly, amid 

 the more pressing occupations of professional life he continued to 

 pursue with eagerness his favourite studies, and soon acquired the 

 reputation of an able and accomplished biologist. His appointment 

 to the chair of Physiology in Dorpat, to which he was called in 1828, 

 enabled him thenceforward to give himself up entirely to scientific 

 work ; and, by the death of Eschscholtz, the sphere of his profes- 



