Density of the Milier. 493 



with 10~ 27 gramme, while the volume is comparable with 

 10" 39 c.c.; so that the density o£ the medium must be of the 

 order I0 12 grammes per c.c. ; 



and the absolute value of the magnetic constant //, for free 

 space will be about 10 u of the same units. 



The electrostatic rigidity of the medium is therefore 

 10 33 dynes per sq. cm.; 



or the absolute value of the dielectric constant k for free 

 space is 10~ 32 cubic centimetre per erg. 



The intrinsic constitutional kinetic energy of the aether, 

 which confers upon it its properties and enables it to transmit 

 waves, is thus comparable with 10 33 ergs per c.c. ; 



or say 100 foot-lbs. per atomic volume. 



This is equivalent to saying that 3 x 10 17 kilowatt-hours, or 

 the total output of a million-kilowatt power station for thirty 

 million years, exists permanently, and at present inaccessibly, 

 in every cubic millimetre of space. 



13. Just as the aetherial rigidity is of a purely electric 

 character, and is not felt mechanically — since mechanically 

 it is perfectly fluid, — so its density is likewise of an electro- 

 magnetic character, and again is not felt mechanically, because 

 it cannot be moved by mechanical means. It is by far the 

 most stationary body in existence; though it is endowed 

 with high intrinsic energy of local movement, analogous to 

 turbulence, conferring on it gyrostatic properties. 



Optically, its rigidity and density are both felt, since optical 



disturbances are essentially electromotive. Matter loads the 



aether optically, in accordance with the recognized fraction 



n 2 — 1 



and this loading, being part and parcel of the matter, 



n 2 ' 



of course travels with it. But it is not a mechanical 

 loading. 



The mechanical density of matter is a very small proportion 

 of the aetherial density ; but the optical or electrical density 

 of matter — being really that of aether affected by the intrinsic 

 or constitutional electricity of matter — is not so small. The 

 relative optical virtual density of the sether inside and 

 outside matter is measured by n 2 ; but it may be really a 

 defect of elasticity, at least in non-magnetic materials. 



Electrical and optical effects may be said to depend 

 upon e. Mechanical or inertia effects may be said to 

 depend upon e 2 . 



Detached and inelastic charges can load the aether optically, 

 quite appreciably; but as regards mechanical loading, the 

 densest matter known is trivial and gossamer-like compared 

 with the unmodified aether in the same space. 



