of the problem of the universe. The first of these steps was taken in 1874, 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[1].
The second step was the discovery of the thermal transpiration of gas, together with the analytical proof of the dimensional properties of matter[2].
The third step was the discovery of the criterion of the two manners of motion of fluids.[3]. 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[4] which directed attention to the possibility 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[5], which led to the
