2 5 S 



NATURE 



[Jan. 15, 1880 



abnormal transverse disturbance produced in the streams 

 of atoms in their passage through the vibrating molecules 

 of luminous bodies. 



Finally, it may be shown that, quite independently of 

 any consideration of the effects of gravity and light, the 

 inference is a necessary one that the constitution of the 

 ether must in principle be that of a gas, because this solu- 

 tion to the problem of the constitution of the ether 

 exhausts the limits of the conceivable : i.e., if any rational 

 solution to the problem or explanation capable of appre- 

 ciation by the reason exists, then it would follow that this 

 must be the true solution to the problem. This will be- 

 come more and more evident on reflecting on the subject. 

 For it is clear that a motion in straight lines is the only 

 motion possible to particles of matter moving freely in 

 space ; for particles of matter cannot of themselves 

 change the directions of their motions. They can only 

 do this at their encounters. Hence the inference is neces- 

 sary that the particles of ether move in straight lines (and 

 therefore that the ether is constituted as a gas). Hence 

 in principle it seems apparent that the above is essentially 

 the only conceivable solution of which the problem of the 

 constitution of the ether admits. It seems remarkable 

 that this fact (important as it is) is not more generally 

 recognised and appreciated. Can this be referable in any 

 ■way to the influence the theory of "action at a distance" 

 has had, and that the endless empty and profitless specu- 

 lations arising therefrom have diverted attention from the 

 subject ? 



It might be said that we have expressly assumed the 

 existence of "particles" (or atoms) of matter in the 

 above result as to the constitution of the ether, whereas 

 some might contend that the ether is not atomic at all 

 My answer to this is, that unless we assume the ether to 

 be atomic, 1 we cannot give any explanation of its proper- 

 ties, and these properties can exist solely in virtue of the 

 explanation that underlies them. In connection with this 

 the following remark of Prof. Clerk Maxwell ("On the 

 Dynamical Theory of Gases," Phil. Trans., 1867, p. 49) 

 may be quoted, as to the point : — 



" In certain applications of mathematics to physical 

 questions, it is convenient to suppose bodies homoge- 

 neous, . . . but I am not aware that any theory of this 

 kind has been proposed to account for the different pro- 

 perties of bodies. Indeed, the properties of a body 

 supposed to be a uniform plenum may be affirmed dog- 

 matically, but cannot be explained mathematically." 



Hence to assume the ether to be anything else than 

 atomic, would be to affirm its properties "dogmatically." 

 If we avoid this, therefore, we must consider it atomic 

 (and therefore a gas) : for (as we pointed out), atoms in 

 free motion can only move in straight lines. It is of 

 course evident that, unless the atoms of ether be in 

 motion, we cannot account for any of its properties, un- 

 less, indeed, we resort to the now practically defunct 

 theory of "action at a distance," and assume the atoms 

 to be endowed with mysterious and occult powers, which 

 renders any explanation impossible, and only increases 

 instead of diminishing the difficulty. 



To illustrate somewhat further the insuperable nature 

 of the difficulty involved, unless we assume the atoms of 

 ether to be in motion in their normal state, I quote the 

 following passage from a lecture by Prof. Tait on "The 



■ It is almost needless to add that the vortex-atom theoryis essentially an 

 atomic theory. Although it assumes a perfect liquid to fill all space, vet 

 this liquid (outside the portions of it that form the atoms) plays the part of 

 pure space, since it is impossible to communicate energy to the liquid out- 

 side the atoms, or to act upon it at all. It is therefore (as far as practical 

 effects are concerned) as if the liquid exterior to the atoms did not exist. 

 The vortex-atom theory does not, therefore, essentially alter (as some might 

 be disposed to imagine) the conceptions of the ancients of indestructible 

 atoms surrounded by space in which they can freely move. The main 

 purpose of the vortex-atom theory is to prove dynamically how atoms can 

 be "elastic" and be capable of executing regular vibrations as the spectro- 

 scope proves (and actually measures the number of vibrations executed per 

 second, in the case of the molecules cf gross matter). 



Position and Prospects of Physical Science," delivered 

 November 7, i860 (p. 15 in pamphlet) :— 



"If we suppose it [the ether] to consist ... of de- 

 tached particles ... we are met by the further difficulty, 

 how do these particles act on each other, and without 

 some such action there could be no transmission ot 

 motion— they are not in contact, there must therefore 

 be something between them to convey the effect. This 

 appears certain, for how can action be conceived as 

 exerted across empty space ? " 



I will merely here remark parenthetically that the fact 

 appears to have escaped notice here that this difficulty is 

 got over by assuming the particles (of ether) to be in 

 motion ; for then the particles can act on each other by 

 direct impact without the necessity for anything "between 

 them to convey the effect." The passage goes on to 

 say: — 



" We must, therefore, have a second medium to fill the 

 interstices between the particles of ether. If this again 

 consist of detached particles, there will be a third required 

 that these may act on each other — and so on. If, then, 

 we would not have an infinite number of different kinds 

 of matter in each element of space, we must suppose one 

 of these — say the ether itself — to be continuous, that is, 

 not consisting of ultimate parts. Hovi vibratory motions 

 could be transmitted through such a substance, it is 

 difficult to imagine — the whole subject is beset with 

 overwhelming difficulties." 



In the above passage the difficulties that attend the 

 assumption of the ether being a continuous substance, or 

 uniform plenum, are well illustrated. It will be seen that 

 the main dilemma vanishes by assuming the particles of 

 ether to be in motion in their normal state. Indeed, this 

 is evidently the only conceivable way of solving the 

 difficulty. 



I would, therefore, venture to suggest that the result 

 above arrived at as a solution to the problem of the 

 constitution of the ether might be worthy of the attention 

 of physicists, especially in its bearing on the explanation 

 of gravity (on the basis of Le Sage's fundamental principle 

 now recognised by several eminent authorities, including 

 Sir W. Thomson) — also in relation to a mode of ex- 

 plaining the transverse vibrations of light, the main idea 

 involved in which was suggested by Prof. Clerk Maxwell. 



Addendum. — I may mention that I have lately re- 

 ceived a book ("Das Rathsel von der Schwerkraft" — 

 Wieweg und Sohn, Braunschweig) through the kindness 

 of the author, Dr. Isenkrahe, of Crefeld, where a theory is 

 applied to the constitution of the ether and to gravity, 

 which resembles in some points that adopted by the 

 present writer. This book bears date 1879, but the MS. 

 was prepared earlier (1877). I may note that a book, 

 "Physics of the Ether" (E. and F. N. Spon), was pub- 

 lished by me in 1S75, where in principle the same theory 

 of the ether as here given is developed, though it was 

 not applied by me to gravity until 1S77. The work of 

 Dr. Isenkrahe contains, in addition, a valuable descrip- 

 tion and criticism of the various attempts to solve the 

 problem of gravitation. Perhaps I may append, for the 

 benefit of those who are interested in the question, the 

 references to some of the chief of these here, viz. : — 



Huyghens' " Discours sur la Cause de la Pesanteur." 

 Leyden, 1690. 



Le Sage's theory 1764, given in "Deux Traites dc 

 Physique mecanique," by Pierre Prevost. 



Sir W. Thomson's development of Le Sage's theory, 

 Royal Society of Edinburgh, 1872, and Philosophical 

 Magazine, May, 1873. 



Schramm, " Die allgemeine Bewegung der Materie als 

 Grundursache der Naturerscheinungen," Vienna, 1872. 



Secchi, "Die Einheit der Naturkriifte " (German edi- 

 tion). Leipzig, 1876. 



These facts may show an awakening to the importance 

 of the problem of gravitation, and I may conclude with 



