4 Davies.—Some Electric and Elastic Analogies. 
I have in each case indicated the sources from whence the formulae 
are derived as well as the general course of the demonstrations by which 
their authors have established them. I have done so partly for the pur¬ 
pose of showing the entirely distinct grounds upon which the demonstra¬ 
tions are based in the two theories, and consequently the greater 
impressiveness and possible meaning of their coincident results, and 
partly in order to call the attention of elementary students of both sub¬ 
jects to a field which seems to be one of considerable promise. It seems 
certain that in this great border region of the elastic and other me¬ 
chanical properties of a medium in which ether, matter, and possibly a 
“tertium quid, electricity” exist, lie some of the greatest problems and 
discoveries of the near future in both chemistry and physics. It is that 
towards which Sir Wm. Thomson, in his Baltimore lectures and various 
papers published since then, has contributed so largely, and in which the 
efforts now making to find a comprehensive theory of physical optics 
have been so ably summarized by Prof. Glazebrook in his Report to the 
British Association for the Advancement of Science (Aberdeen meeting, 
1885). It is the complete theory of the ether embracing electro-magnet- 
ism and optics, towards which our present knowledge has made only a 
small advance. 
These close analogies between elasticity and electro-statics or magnet¬ 
ism have led me to place side by side a few of the well known formulae 
of both of these great fundamental branches of physics, with their de¬ 
rivations. In this manner the points of resemblance become more ap- 
solid in which each element has a certain resultant angular displace¬ 
ment, representing in magnitude and direction the force at this point 
produced by a magnetic body; and the third represents in a similar 
manner the forces produced by any portion of a galvanic wire; the di¬ 
rections of the force in the latter case being given by the axis of the re¬ 
sultant rotations impressed upon the elements of the solid.” 
“Let there be an elastic body of exceedingly small density, and let 
there be a tubular portion of it porous, but with the same aggregate 
rigidity as that of the continuous elastic matter round it. Let the pores 
be filled with a dense viscous fluid, and let this fluid be forced, by aid of a 
piston or otherwise, to move through the tube. The pull of the fluid 
upon the porous solid will produce static rotational displacement exactly 
proportional to the continued rotatory motion which we had in the case 
of the viscous fluid. Some of the most interesting practical problems 
of electro-magnetic induction can be dynamatically realized, as it were, 
in model, by following out this idea; in fact, if we had nothing but 
electricity and ether, the thing would be done. If it were not gross 
ponderable matter that we are forced to consider, I should be perfectly 
satisfied with the problem of electro-magnetic induction, by taking the 
electricity as a viscous fluid, and ether an elastic solid, porous in some 
places, and continuous or non-porous elsewhere.” See in particular ar¬ 
ticle XCIV., Reprint of Mathematical and Physical Papers, Vol. III. 
