397-] CONSTRAINED SYSTEM. 225 



variable system forms the basis for the investigations of mathematical 

 physics, i.e. for the theory of elastic bodies, of fluid and liquid 

 motion, of heat, light, electricity, and magnetism. The following 

 works are particularly recommended as introductions to this subject : 

 THOMSON AND TAIT, Natural Philosophy, Vol. L, parts i and 2, Cam- 

 bridge, University Press (New York, Macmillan), new edition, 1890; 

 W. VOIGT, Elementare Mechanik als Einleitung in das Studium der 

 thforetischen Physik, Leipzig, Veit, 1889 ; G. KIRCHHOFF, Vorlesungen 

 uber mathematische Physik ; Mechanik, 3te Auflage, Leipzig, Teubner, 

 1883. 



PART 111 15 



