Jan. 15, 1880] 



NATURE 



257 



and many other well known independent facts render this 

 inference necessary. The fact that gravity is proportional 

 to mass, on the basis of the dynamical theory (first started 

 by Le Sage) also renders it essential to conclude that 

 gross matter possesses an open structure [so that the 

 atoms producing gravity can penetrate and act upon the 

 interior of bodies]. If we admit this, and figure to our- 

 selves the streams of ether atoms passing in all directions 

 freely through the open structure of gross matter, and 

 further, if we conceive the molecules of gross matter to 

 be in a state of vibration (of regular periods, as proved by 

 the spectroscope), then it is evident that these streams of 

 ether atoms during their passage can, from the very nature 

 of the case, be solely effected by the transverse component 

 of the motion of the molecules of the luminous body. It 

 is much as if the meshes of a sieve were in vibration, and 

 a continuous stream of fine particles of sand (impelled by 

 a current of air) were urged through it, when in however 

 many different directions the filament forming the meshes 

 of the sieve might be conceived to be vibrating, the sand 

 particles that passed through in the onward stream could 

 be only affected by the transverse component of the 

 motion of the meshes. So the atoms of ether in 

 their passage through the vibrating molecules of gross 

 matter are solely affected by the transverse component 

 of the motion of the molecules. The ether atoms passing 

 through the open structure of gross matter would be thus 

 periodically deflected (or the ether atom itself thrown into 

 vibration or rotation), and as the transverse impulses 

 (whatever their exact nature) thus received by the stream 

 of ether atoms would be perfectly ryhthmicai or periodic, 

 in harmony with the known periodic vibrations of the 

 molecules through which the ether atoms pass, the trans- 

 verse pulsatory or periodic nature of light would thus be 

 produced. This view would also seem to be capable of 

 surmounting in a very simple manner the difficulty that 

 there has been in conceiving how the ether can transmit 

 transverse vibrations to great distances without sensible 

 loss of energy by dissipation. For it is evident that an 

 ether atom after having passed through a luminous body 

 and received energy from it, would have nothing ' to give 

 that energy (say vibration or rotation) to during its 

 transit, since, by assuming the ether atom small, we may 

 conceive its mean path as long as we please ; so, there- 

 fore, the energy carried by the ether atom from the 

 luminous body could not possibly be diss.pated during the 

 transit of the atom, but this energy would be carried 

 intact by the ether atom (through its normal motion of 

 translation) until the distant object is reached, where the 

 energy is given up in the form of heat and light. The 

 normal motion of translation possessed by the ether atom 

 performs the part of simple carrier of the energy received 

 by the atom from the luminous body. 



It might possibly be thought at first sight that this 

 theory had some resemblance in principle to the emission 

 theory of light, but this is evidently not the case, as no 

 atoms are emitted by the luminous body, but simply the 

 atoms of ether in their normal state of translator)' motion 

 pass through objects in streams equally in all directions 

 ■ — the ether being regarded simply as a gas (according to 

 the modern kinetic theory) with atoms of very long free 

 path. It is a known mathematical fact that no conse- 

 quence how close the atoms of ether may be together 

 (i.e., no consequence how many in unit of volume) their 

 mean path may become as great as we please, by simply 

 conceiving the atoms adequately small. It further follows 

 from the known principles investigated in connection with 

 the kinetic theory of gases, that these atoms will of them- 

 selves automatically adjust their motions so as to move 

 with perfect uniformity or equally in all directions ; this 

 adjustment being of such a rigid character that if the 



1 This holds equally true, whether we conceive space as empty, or space to 

 be filled with a perfect (frictionless) liquid that plays the exact part of empty 

 space, in so far as it is known to be impossible to operate upon or communi- 

 cate energy to such a liquid. 



atoms were imagined to be disturbed or made to move in 

 the most chaotic manner, they would, when left to them- 

 selves, instantly correct the irregularity, and return to the 

 above regular form of motion, i.e., so that the atoms move 

 equally m all directions. 1 1 follows from this, therefore, that 

 if we lake any given point (such as where a luminous body 

 is situated), the atoms of ether will "radiate" from and 

 to this point along all the imaginary radii of a sphere 

 described from this point as a centre ; so that those ether 

 atoms which hive passed through the luminous point 

 (and have carried energy off with them) will diminish in 

 number (per unit of spherical area) as the square of the 

 radial distance from the luminous point, the energy, there- 

 fore, diminishing in the same ratio, which is the "law" 

 of light. The "law" of gravity (which is found also to 

 diminish as the square of the distance) maybe accounted 

 for on the same principle. 



It has been shown by the present writer (in the papers 

 published in the Phil. Mag. previously alluded to) that in 

 accepting Le Sage's ingenious sheltering principle as the 

 fundamental basis of the explanation of gravity, there is 

 no necessity for admitting any of his postulates regarding 

 the particular motions of the atoms (corpuscles) required 

 to produce the result. For it may be shown that the whole 

 of the conditions requisite for gravity will automatically 

 fulfil themselves by simply admitting the existence of a 

 body in space, constituted according to the kinetic theory 

 of gases (and whose atoms have an adequately long free 

 path). There is no necessity to suppose, with Le Sage, 

 the existence of " ultramundane corpuscles," or that the 

 atoms producing gravity come from outside the bounds of 

 the visible universe, so that a continuous supply of matter 

 from without is necessary to maintain gravity within 

 the confines of the visible universe. On the contrary, 

 the conditions are satisfied by merely supposing the 

 universe to be immersed in a gas, which, as a -whole 

 (like any other gas) is at rest. The motion (in streams) 

 requisite for gravity takes place solely within the 

 range of free path of the atoms of the gas ; just (as is 

 known) in every ordinary gas the atoms within the range 

 of free path are moving in streams equally in all direc- 

 tions. The only difference is that in the case of the ether, 

 on account of the smallness of the atoms (which is in 

 harmony with their high velocity), the range of free path 

 is great— equal to the range of gravity. We have no 

 proof that the range of gravity extends across stellar dis- 

 tances, and there is clearly no necessity for assuming it 

 to prevail over greater distances than observation war- 

 rants. By the explanation of gravity by the physical 

 theory, the remarkable and anomalous distinction between 

 two kinds of matter ("ponderable" and "imponder- 

 able") vanishes. Matter is shown of its essence to be all 

 alike, "ponderability," or the tendency to approach, not 

 being an occult or magic quality, but simply an effect 

 dependent on differing dynamical conditions, 1 and the 

 variation of the intensity of which as the square of the 

 distance it is as necessary to account for dynamically as 

 in the analogous case of light. 



It appears, therefore, from the above considerations, 

 that the same medium shows itself to be capable of 

 accounting for, in their essential groundwork, the pheno- 

 mena of both gravity and the propagation of light. 

 The theory of gravity is based upon the well-known 

 sheltering principle of Le Sage, which has already found 

 favour with some eminent physicists. The normal trans- 

 latory motion of the atoms of the medium produces 

 gravity, and this motion serves as a vehicle for the propa- 

 gation of light, while the light itself consists in the 



■ The fact of the property of "ponderability" having been attributed to 

 r as an cccult quality (not an effect depending on dynamical con- 

 d.ti n ). lias naturally brought the ether— which d 



property— into direct contrast with gross matter, as if it were an 

 substance, of its essence distinct from gross matter. 1 his circumstance nas. 

 no d ubt naturally contributed to produce a distaste for the study of the 

 ether and to cause some to treat this magnificent physical agent IS it- ,t 

 were des red rather to ign. re than to take a rational interest la Us existence- 



