N/A (1886). Dilatancy Nature, 33 (853), 429-430 DOI: 10.1038/033429b0

I encountered the word “ether” which apparently did not mean the organic reagent when I was reading a short comment on O. Reynolds’s lecture on dilatancy published on Nature in 1886. It is very interesting to notice that this rheological phenomena had originally been conceived before the concept of “ether” was abandoned in physics.

This comment was published a year after O. Reynolds’s first formal publication on dilatancy on Phil. Mag. on 1885, where the word “dilatancy” was, for the first time, coined and defined as volume increase during deformation. When a material consist of many close packed hard spheres is forced to deform, because the spheres need extra space to rearrange their positions, the volume of the material has to increase, otherwise the material is not deformable. In his publication, Reynolds explained that the intention to conceive this physical process originate from the convention of using spheres as a model of molecules to solve fluid mechanical problems. While the normal liquids were explained by various models of deformable spheres, it is logically derivable to consider cases when these spheres are rigid.

Then to my surprise, the finding of dilatancy mechanism even at once explained the ether concept to a further extent!

In the beginning of the 1886 comment published on Nature, it was described that the finding about dilatancy was

the result of an endeavour to conceive the mechanical properties a medium must possess in order to act the part of the all-pervading ether — transmitting waves such as light, but not such as sound, allowing free motion of bodies, causing distant bodies to gravitate, and casing forces like cohesion, elasticity, and friction between adjacent molecules, together with electricity and magnetism.

On a larger scene, however, 1886 was the very year when the common belief in ether was just about to melt. After J. Maxwell published his Treatise on Electricity and Magnetism in the 1870s, according to what the Maxwell equations predict, the properties of the ether contradicted with itself. Using the expression from Wikipedia.org,

it had to be a fluid in order to fill space, but one that was millions of times more rigid than steel in order to support the high frequencies of light waves. It also had to be massless and without viscosity, otherwise it would visibly affect the orbits of planets. Additionally it appeared it had to be completely transparent, non-dispersive, incompressible, and continuous at a very small scale.

However, the mechanism of dilatancy which allows a possible condition for a low viscous liquid to suddenly become rigid, eased to some extent the above paradox of ether. This is what the comment on 1886 Nature suggested:

[Reynolds's] lecture then indicated how the property of dilatancy in a continuous medium would render it capable of causing an attraction between bodies at the distance, like gravitation, and cohesion, and elastic forces between bodies close together; how the ability of the grains to rearrange at the free surface would allow bodies to move freely in the medium which, if in a state of agitation by transverse waves in all directions, would transmit waves like those of light, but not like sound, and which if consisting of grains of two different sizes or shape, would give rise to phenomena resembling those of electricity.

However, the author of this comment also bewared that

promising as this dilatant hypothesis of ether was, it could not be taken as proved until it had been worked out in detail.

Furthermore,

[t]he property of dilatancy once recognised was, however, independent of any hypothesis, and seemed to have opened up a new field for philosophical and mathematical research quite independent of the ether.

In fact immediately after that, the first null result from the experiments to detect ether using light, i.e. the Michelson-Morley experiment, released, followed by more confirmation with lower error level. Soon by the first half of the 20th century, the room for the ether concept was nearly eliminated by experiments and reasoning.

As a result, the dilatancy concept lived much longer than the ether concept and showed its importance in the wellbeing of human (liquid body armor).