a space without inequalities across the surface beyond which the inequalities are in closest order ;
That the aberration of light results from the absence of any appre- ciable resistance to the motion of the medium when passing through matter.
8. It may be somewhat out of the usual course to describe the results of a research before any account has been given of the method by which these results have been obtained ; but in this case the fore- going sketch of the purely mechanical explanation of the physical evidence in the universe by the granular medium has seemed the only introduction possible. And even so it is not with any idea that this introduction can afford any preliminary insight as to the methods by which these results have been obtained.
Certain steps, as it now appears, were taken for objects quite apart from any idea that they would be steps towards the mechanical solu- tion of the problem of the universe. The first of these steps was taken with the object of finding a mechanical explanation of the sudden change in the rate of flow of the gas in the tubes of a boiler when the velocity reached a certain limit ; perhaps this would be better described as a step towards a step.*
The second step was the discovery of the thermal transpiration of gas together with the analytical proof of the dimensional properties of matter.!
The third step was the discovery of the criterion of the two manners of motion of fluids, \ and it was only on taking the fourth step, namely, the study of the action of sand, which revealed dilatancy as the ruling property of all granular media which directed attention to the possi- bility of a mechanical explanation of gravitation. In spite of the apparent possibility all attempts to effect the necessary analysis failed at the time.
There was, however, a fifth step : the effecting of the analysis for viscous fluids, and the determination of the criterion, || which led to the recognition of the possibility of the analytical separation of the general motion of a fluid into mean varying motion, displacing momentum, and relative motion without mean momentum ; and this suggested the possibility that the medium of space might be granular, the grains being in relative motion, and at the same time being subject to varying mean motion. And this has proved to be the case.
At the same time it became evident that it was not to be attacked by any method short of the general equations of a conservative system
- ' Manchester Lit. and Phil. Soc.,' 1874-5, p. 7.
f ' Phil. Trans.,' 1879.
I ' Phil. Trans.,' 1883.
' Phil. Mag.,' 1885.
|! ' Phil. Trans.,' 1895.
