Return to Physics of the Ether

91. The Static Effects of the Ether.— We will return here "to the consideration of the static effects of the ether as exhibited in the phenomena of " cohesion," chemical union, &c, i. e. the general phenomena of the aggregation of molecules.

As an illustrative example having a general application, we may take the case of a metallic bar submitted to a tensile strain.

62

Though in reality it is impossible to apply a tensile strain to matter, since matter consists of discrete or wholly unconnected parts (molecules and particles) separated by empty space, and it is impossible to direct a strain across empty space, or to put' space under strain, still the term " tensile strain, in contradistinction to " compressive strain," may be convenient in practice to denote the particular direction in which it is desired to produce motion.

92. If b, c, d, &c, Fig. 6 (i.), represent any line of molecules in the direction of the length of a metallic bar, these molecules being in equilibrium with the ether pressure, and at a certain distance apart, which remains constant so long as the vibrating energy (" temperature ") of the bar is kept constant. Then when the bar is said to be under a " tensile strain," the direction of the movement of the molecules is from each other, or the ends of the bar are moved to a greater distance apart We will consider, therefore, any single molecule b, and suppose it to be moved to a greater distance from the next molecule e, taking up the new

position V (n.), it being supposed that the Fig. 6. farther end of the bar is fixed. Then the

(I) £ • £• J equilibrium of the ether pressure is disturbed

by this movement of the vibrating molecule

(II) ## 5 # ? m *° a new position, the energy of the sta- f e>ac o tionary vibration of the ether column inter-

(TirW** • t cepted between b and c being reduced by * ' f e>d> o' o the increase of the distance of the two molecules, the effect being that the pressure (TV) £, •. *y *> J. exerted by the vibrating column upon the

opposing halves of the molecules V and e is reduced, the pressure of the column being necessarily reciprocal, or equal for each molecule, owing to the mutual reflection of the pulsations. The ether pressure upon the opposite sides of the molecule e is therefore no longer equal, the lengths of the two oscillating ether columns at opposite sides of the molecule being unequal, the molecule is therefore driven into a new position e' (in.), or the molecule is moved by the ether pressure, until by its increased distance from the next molecule d, the ether pressure upon the opposite sides of the molecule c' becomes again equal, the same considerations applying to all the molecules of the bar. The effect of moving the end molecules of the bar outwards (as in the case of a "tensile strain") has, therefore, the result of causing all the vibrating molecules of the bar to recede to uniformly increased distances (iv.), this uniform distance of the vibrating molecules being the physical condition required for uniformity in the ether pressure, by which the positions of equilibrium of the molecules are regulated. During the time the strain lasts, therefore, the value of the ether pressure between the opposed vibrating molecules of the bar (i. e. where the molecular distances are abnormally increased) is less than the

63

normal ether pressure existing outside the bar, by an amount which represents the static value of the strain.

The mode of action in the case of a tensile strain, in some respects at least, although the analogy is evidently not strict, admits of rough F ra- 7.

illustration, if we suppose a glass tube, / , \ | , , , l | , Fig. 7 (1), containing a series of sliding ' Invrvop

discs, Z, m, n, o, p 9 fitting air-tight in (g>— - - g ? i i -tu — . the tube, the spaces between the discs VrnTnT^p'

being supposed occupied by air at ordinary atmospheric density, the discs being thus in equilibrium, or the air pressure, i. e. the energy of the impacts of the air molecules upon the opposite sides of each disc is the same. If, then, the two extreme discs be moved outwards, as occurs in the case of a tensile strain, the remaining discs will all take up new positions of equilibrium T, rnl,n!,c!, jf (2), such that the intervening distances become again equal to each other, this being the condition required to satisfy the equality in the air pressure upon the opposite sides of the discs, the whole system being uniformly distended, and returning to its previous position of equilibrium when the strain ceases.

93. There would be, perhaps, a natural tendency to assume that because the density of the ether is so extremely low, the distance of its particles must be proportionately great, and that, therefore, this agent would not be physically adapted to control steadily and forcibly the molecules of matter in positions of stable equilibrium, such as to control the molecules of a steel bar, for example. It is, therefore, well to keep practically in view the fact that although this agent has a very low density, yet its component particles may be in extremely close proximity, or the agent may be extremely compact and well adapted to exert a perfectly uniform pressure about a molecule, for there is no limit to the degree of close proximity into which the particles of the medium may be brought by the simple means of an extreme state of sub- division of the matter forming the medium. Since this extreme state of subdivision is undoubtedly the fact in the case of the ether, it is well, therefore, in dealing with the phenomena of u cohesion " or the static effects of the ether generally, to realize clearly and practically the ether as an extremely close and com- pact body, although possessing an extremely low density. In other words, although the density, i. e. the volume of matter relatively to the volume of space, is small in the case of the ether, still there is nothing to prevent the particles from being in extremely close proximity to each other, under the simple condition of an extreme state of subdivision, the agent thus becoming very close and compact, and mechanically well adapted to control forcibly the molecules of matter in positions of stable equilibrium.

64