W = Mg

Abstract

I HAD read Mr. Slate's letter (NATURE, vol. xliv. p. 445), and admired it; moreover, I found myself in agreement with him. But it seems to me strange that Prof. Greenhill should approve of it. For Mr. Slate takes as his gravitational unit of force “the weight of one pound under circumstances specified…(locality, vacuum).” Surely this implies that he agrees with the theorists (Prof. Greenhill's foes) when they say that “the weight of a given body depends on the local value of g.” Prof. Greenhill, on the contrary, speaking of goods, says that “the weight cannot be said to vary with the local value of g” (NATURE,Vol. xliv. p. 493), I would ask him, then—