"Let us now turn to the Moon. In the first place the action of the Earth in raising tides in the Moon explains at once how she now turns always the same face towards us, or rotates on her axis once a month. When she was perhaps much hotter and perhaps more plastic and certainly younger, the Earth must have raised very considerable tides in the solid boy as well as in her oceans, if ever she had oceans. On these the Earth would act as the Moon acts now on the Earht tides, but more considerably. The resultant action would be a force not through her centre, but a 'sideway' force opposing her spin round her axis; acting in fact as a brake until the spin was reduced so far that brake and wheel went round together, the Moon's period of rotation coinciding with the month. The tides on the Moon, tides in the slightly plastic body, are always now at the same parts of her surface, directly facing and directly opposite to the Earth. In the second place there is a reaction of the Earth's tides on the Moon equal and opposite to the action of the Moon on the Earth's tides. ..."