H is the head, bearing the tentacles T1 and T2, of which the upper pair have the eyes, E.

The two thermometers are indicated as T1 and T2 and are inserted in the ingoing and outgoing water respectively.

Then to every such strip will correspond a strip of equal length x of the figures described by T1 and T2.

In other words, the ratio of r3 to T2 for every planet is the same.

Let v1 denote the velocity of T1 at any given instant; v2 that of T2.