ON LATER VIEWS OF THE CONNECTION OF ELECTRICITY AND 



MAGNETISM, 



EEVIEW OF MATHEMATICAL THEORIES. 

 By Professok Helmholz. 



[From the London Academy.] 



The problem of determining tlie primary causes of tbe so-called elec- 

 tro-magnetic and electro-dynamic i)lienomena is connected intrinsically 

 with some of the most important theoretical questions of natural phi- 

 losophy regarding the general character of force and the essential 

 attributes to be ascribed to the medium which fills space. The subject, 

 therefore, has attracted the . attention of natural philosophers and 

 mathematicians since the time of Oersted's first discovery regarding 

 the deviation of a magnetic needle by a galvanic current, in 1820, till 

 the present moment j and this attention has grown even the more 

 intense and concentrated the more our knowledge of the experimental 

 facts approached to completeness. The force of gravitation, Newton's 

 grand conception, has been hitherto the model for nearly all the scien- 

 tific hypotheses by which philosophers have striven to connect and to 

 explain the various kinds of physical and chemical phenomena. Hy- 

 I>otheses of this kind, based on the assumption of forces acting between 

 two material points along the straight line of their junction, either 

 attracting or repelling, the intensity of which is independent of time and 

 velocity, but dependent on the distance of the two points, have been 

 applied with great success, not only to the effects of celestial and ter- 

 restrial gravity, but also to those of elasticity in rigid, fluid, and gaseous 

 bodies, including the phenomena of sound and light. In the theory of 

 heat and chemical actions, it appears highly probable that we have to 

 do with forces of the same kind, although of a much more limited 

 sphere of activity. In consequence of the extreme complexity of 

 causes and conditions, only very small parts of these branches of 

 science have been worked out so far that the connection between actual 

 phenomena and elementary forces can be traced the whole way and 

 deduced by mathematical analysis. The nearest analogy with the laws 

 of gravitation we find in the jjhenomena of electricity and magnetism 

 as long as these agents are in a state of repose and equilibrium. We 

 find the same law of action at a distance, and the inferences derived 

 from this law are even more open to controlling experimental measure- 

 ments of the highest degree of precision than those of gravitation, or 

 of the molecular forces, which keep up the motion of heat, produce 

 chemical combinations, and are the alternate cause of elasticity. The 

 very existence of the electro-static and magnetic forces must have 

 increased a good deal the tendency of natural philosophers to generalize 

 this kind of hypothesis, which answered so well to the requirements of 



