But I must repeat that this conveyance of light by moving matter is an effect due to the material load only; it represents no disturbance of the ether of space. Fresnel's law, in fact, definitely means that moving transparent matter does _not_ appreciably disturb the ether of space. Direct experiment, as recorded in Chapter V, shows that close to rapidly-moving opaque matter there is no disturbance either. I regard the non-disturbance of the ether of space by moving matter as established. FOOTNOTES: [10] _Philosophical Magazine_, Dec., 1887. [11] _Archives Néerlandaises_ (1869), Vol. IV, p. 443, or _Nature_, Vol XXVI, p. 500. Also Chapter IV above. SUMMARY. The estimates of this book, and of _Modern Views of Electricity_, are that the ether of space is a continuous, incompressible, stationary, fundamental substance or perfect fluid, with what is equivalent to an inertia-coefficient of 10¹² grammes per c.c.; that _matter_ is composed of modified and electrified specks, or minute structures of ether, which are amenable to mechanical as well as to electrical force and add to the optical or electric density of the medium; and that elastic-rigidity and all potential energy are due to excessively fine-grained etherial circulation, with an intrinsic kinetic energy of the order 10³³ ergs per cubic centimetre. APPENDIX 1 ON GRAVITY AND ETHERIAL TENSION In the arithmetical examples of Chapter IX we reckon merely the force between two bodies; but the Newtonian tension mentioned in Chapter VIII does not signify that force, but rather a certain condition or state of the medium, to variations in which, from place to place, the force is due. This Newtonian tension is a much greater quantity than the force to which it gives rise; and, moreover, it exists at every point of space, instead of being integrated all through an attracted body. It rises to a maximum value near the surface of any spherical mass; and if the radius be R and the gravitational intensity is _g_, the tension at the surface is T₀ = gR. At any distance _r_, further away, the tension is T = gR²/r. This follows at once thus:-- Stating the law of gravitation as F = γmm´/r², the meaning here adopted for etherial tension at the surface of the earth is T = ∫{R,∞} γE/r² dr = γE/R; so that the ordinary intensity of gravity is g = -dT/dR = γE/R² = 4/3πργR. Accordingly, near the surface of a planet the tension is T₀ = gR, or for different planets is proportional to ρR². The velocity of free fall from infinity to such a planet is √(2T₀); the velocity of free fall from circumference to centre, assuming uniform distribution of density, is √(T₀); and from infinity to centre it is √(3T₀). Expanding all this into words:--