316 
14. Mos so. Les lois de la fatigue étudiées dans les muscles de l’homme. 
Ibid. XIII, 1890. 
15. Patri zi. Oscillations quotidiennes du travail musculaire etc. Ibid. 
XVII, 1892. 
16 Scripture. Researches on voluntary effort. Stud, from Yale Psych. Lab., 
IV, 1896, 
17. Treves. Sur les lois du travail musculaire. Ar. it. de Biologie, XXIX 
(1898), XXX (1898), XXXIII (1900). 
18. Idem, Sur les conditions qui déterminent le rythme spontané etc. Compte 
rendu du V-e Congrès intern, de Physiol., ibid. XXXVI (1901) 
19. Idem. Modifications à l’ergographe. Ibid. 
20. Idem. Ueber den gegenwärtigen Stand unseres Wissens, die Ergogra- 
phie betreffend. Pflüg. Ar., t. 88, 1901. 
21. Zoth. Ergographische Versuche über die Erholung des Muskels. Ibid., 
t. 111. 1906. 
20. M. LADISLAS NATANSON m. t. Studya nad teoryq elektromagnetycznq 
dyspersyi i extynkcyi w ciaîach gazowych. ( On the Electromagnetic 
Theory of Dispersion and Extinction in Gaseous Bodies ). (Sur 
la théorie électro-magnétique de la dispersion et de Vextinction dans les corps 
gazeux). 
It is now generally accepted that molecules of material bodies 
contain "electrons” or small corpuscles having definite electric char¬ 
ges. The vibrations of such corpuscles about their positions of equi¬ 
librium must be modified when subjected to periodically varying 
electromagnetic forces; we shall therefore be enabled to explain the 
phenomena of dispersion and extinction on the basis of the electronic 
hypothesis; and from a detailed study of dispersion and extinction 
we can expect to derive a considerable amount of guidance as to 
the properties which are to be attributed to electrons, and to forces 
acting on electrons. 
§ 1. In what follows we shall consider a homogeneous isotropic 
body composed of a very large number of molecules. We suppose 
that every molecule can be treated as an independent system; we 
adopt, however, the usual fundamental assumption generally admitted 
in Molecular Theories according to which independent molecular 
quantities when averaged over finite portions of the medium lead 
to values which are perfectly definite and regular. 
Let us write l for the mean distance between neighbouring mo¬ 
lecules which we define thus: 
