218 ANNUAL REPOET SMITHSONIAN INSTITUTION, 1913. 



is always produced in ultimate particles situated in the magnetic 

 field, and its law is a differential law expressing the relation of 

 cause and effect between the existing conditions and their causative 

 predecessors in each ultimate particle of the space. It is from the 

 interaction between all the ultimate particles of the magnetic field 

 in the so-called integral that the effects at a distance result. Maxwell 

 established the laws of effect from point to point of electromagTietism 

 (or differential laws of the electromagnetic field), which with an 

 admirable simplicity not only explained the electromagnetic phe- 

 nomena formerly known (which the laws of effect at a distance were 

 equally capable of doing), but did much more; they predicted, in- 

 deed, the propagation of electric vibrations through space in the 

 form of electromagnetic rays. The luminous rays appeared thus as 

 electromagnatic rays. Hertz obtained, with purely electromagnetic 

 resources, electromagnetic rays of great wave length, and Marconi 

 has utilized these same rays in wireless telegraphy. Thus it is 

 that one of the greatest and most difficult advances in the theory, 

 the transition from laws of effect at a distance to theories of effect 

 from point to point, led immediately to a great technical advance. 



At that time (more than 20 years ago), many physicists. Hertz 

 and Mach in particular, recognized that the real object of the theory 

 was to explain physical phenomena by differential laws, a task which 

 seemed to pass much beyond the attainable, but it has been in large 

 part satisfactorily performed,^ since at present the law of gravitation 

 itself can be expressed in the form of a law of effect from point to 

 point.- The end sought in this connection consists in dethroning the 

 old corpuscular and mechanical theories still so full of vigor. The 

 list of facts brought forth by the two contending parties increases in 

 length from year to year and the struggle between phenomenalistic 

 investigation and mechanical investigation is waged on a field of great 

 extent, embracing almost the entire domain of the exact sciences. The 

 combat centers around the question of the nature of light and of the 

 cathode rays.^ The new theory of gravitation is only a partial victory 



1 G. Jaumann, A complete system of physical and chemical differential laws, Sitz- 

 ungsber. K. Akad. Wiss. Wien, Math.-Naturwiss. Kl., vol. 120, pt. 2a, 1911, pp. 385-530. 



" G. Jaumann, The theory of gravitation, Sitzungsber. K. Akad. Wiss. Wien, Math.- 

 Naturwiss. Kl., vol. 121, pt. 2a, 1912, pp. 95-182. 



3 The majority of physicists still subscribe to the emission theory of cathode rays (the 

 corpuscular or emissional theory) and there is a tendency, under the leadership of Einstein 

 and Planck, towai-d giving up finally the essential features of the classical theory ami 

 going back to a sort of emission theory of light. 



Regarding the undulation theory of cathode rays and the phenomalistic undulation 

 theory of light in dispersion media, see G. Jaumann, The electromagnetic theory (Sitz- 

 ungsber. K. Akad. Wiss. Wien, Math.-Naturwiss. Kl., vol. 117. pt. 2a, 1908. pp. 379-543). 

 which paper was rejected by the editors of the Annalen der Physik in 1908 and in 1911 

 was honored by a prize by the Imperial Academy of Sciences in Vienna. See also E. 

 Lohr, The boundary conditions in G. Jaumann's electromagnetic theory (Sitzungsber. K. 

 .\kad. Wiss. Wien, Math.-Naturwiss. Kl., vol. 120, pt. 2a, 1911, p'p. 1503-1567, and vol. 

 121, 1912, pp. 633-678. 



