Furthermore there are different types of such convergence to simplicity.

For example, we can converge as above to the limiting character expressing nature at an instant within the whole volume of the train at that instant, or to nature at an instant within some portion of that volume--for example within the boiler of the engine--or to nature at an instant on some area of surface, or to nature at an instant on some line within the train, or to nature at an instant at some point of the train.

In the last case the simple limiting characters arrived at will be expressed as densities, specific gravities, and types of material.

Furthermore we need not necessarily converge to an abstraction which involves nature at an instant.

We may converge to the physical ingredients of a certain point track throughout the whole minute.