When this second stratum has reached its destined position—or while approaching it—a third still inferior exertion of the force, or a third inferior force of a similar character—the number of atoms emitted being in _all_ cases the measure of the force—proceeds to deposit a third stratum upon the second:—and so on, until these concentric strata, growing gradually less and less, come down at length to the central point; and the diffusive matter, simultaneously with the diffusive force, is exhausted. We have now the sphere filled, through means of irradiation, with atoms equably diffused. The two necessary conditions—those of irradiation and of equable diffusion—are satisfied; and by the _sole_ process in which the possibility of their simultaneous satisfaction is conceivable. For this reason, I confidently expect to find, lurking in the present condition of the atoms as distributed throughout the sphere, the secret of which I am in search—the all-important principle of the _modus operandi_ of the Newtonian law. Let us examine, then, the actual condition of the atoms. They lie in a series of concentric strata. They are equably diffused throughout the sphere. They have been irradiated into these states. The atoms being _equably_ distributed, the greater the superficial extent of any of these concentric strata, or spheres, the more atoms will lie upon it. In other words, the number of atoms lying upon the surface of any one of the concentric spheres, is directly proportional with the extent of that surface. _But, in any series of concentric spheres, the surfaces are directly proportional with the squares of the distances from the centre._[2] [2] Succinctly—The surfaces of spheres are as the squares of their radii. Therefore the number of atoms in any stratum is directly proportional with the square of that stratum’s distance from the centre. But the number of atoms in any stratum is the measure of the force which emitted that stratum—that is to say, is _directly proportional_ with the force. Therefore the force which irradiated any stratum is directly proportional with the square of that stratum’s distance from the centre:—or, generally, _The force of the irradiation has been directly proportional with the squares of the distances._