M. Henrici on the Theory and Application of Electricity, 167 



Magnetism exhibits the remarkable property of being retained 

 or absorbed by no other bodies than the few magnetic metals, 

 whilst it is diffused through these comparatively slowly, and 

 in a manner more analogous to heat. Consequently there is 

 no conduction of magnetism at all resembling the conduction 

 of electricity. 



If the appearancesof light, heat, electricity and magnetism, 

 are phaenomena of motion, we must arrive at the conclusion 

 that their exceedingly rapid mode of propagation essentially 

 depends upon motion of an imponderable matter (aather), their 

 slow diffusion being essentially dependent on the movements 

 of the atoms of the bodies. An analogy between magnetism 

 and heat consists in the rays emanating from the former prin- 

 ciple being absorbed by the magnetic metals, these thus be- 

 coming magnetized, just as bodies become warmed by the ab- 

 sorption of heat ; but there is this difference between the two 

 agents, viz. that there are but few bodies capable of absorbing 

 the magnetic rays, whilst there is scarcely one which is not 

 able to absorb those of heat. Consequently nearly all bodies 

 may be regarded as completely pervious to the former rays. 



3. If we place two equal-sized plates of copper and zinc 

 upon one another, and after contact separate them, when 

 tested by a delicate electrometer they are both electrical, this 

 occurring only after contact. From this it has been concluded 

 that the dissimilar electricities evolved by the contact of he- 

 terogeneous metals neutralize one another at those parts where 

 they are in contact, and that a comparatively small portion of 

 them is set in motion. This retention in very good conductors 

 is unintelligible, if no other forces were exerted : these effects 

 however are evidently those of condensation, as Peclet long 

 since proved by experiment; he showed that all smooth me- 

 tallic surfaces, when in contact, even without intervening layers 

 of varnish, act as condensers. In fact, in the present case, 

 the same effect would be evident if the contact of the zinc with 

 the copper plate occurred at a few physical points only (pro- 

 bably when their surfaces are perfectly smooth, and they are 

 lightly placed upon one another, there is no real contact): 

 this agrees with what we observe, that the effect is weaker in 

 proportion as the surfaces in action are less. Thus the expe- 

 riment by no means justifies the supposition, that the electri- 

 cities set free by the contact of heterogeneous metals neutralize 

 one another at the place of contact ; it is rather natural to 

 suppose that they possess freedom of motion. The conse- 

 quence of this will be, that from the almost perfect conduction 

 exerted at the place of contact, they will for the greater part 

 combine again, and that a very small portion of them only 



