Explanatory

Abstract

I MUST ask you, in common fairness, to allow me to protest against P. G. T.'s mistaken statement (vol. xix. p. 71) respecting a sentence which he quotes without the explanatory context. The moving force exerted by the earth on the moon as a whole is of course precisely equal to the moving force exerted by the moon on the earth. I had not to learn this from P. G. T., but had said so in so many words. But the moving force exerted by the earth on a given amount of matter in the moon is eighty-one times greater than the moving force exerted by the moon on an equal amount of matter in the earth. P. G. T. will scarcely deny this, and he cannot deny that the whole statement from which he quotes one sentence meant this, and this only. Nor, if he did, would any one who has read the chapter on the moon's motions in my treatise on the moon, believe such a statement.