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The Use of the Words “Weight” and “Mass”

Nature volume 13, page 484 | Download Citation



I WILL supplement Mr. Bottomley's authorities for the meaning of gravity by others which will he perhaps considered more relevant. Maupertuis, “Figure de la Terre,” Paris, 1738, writes:—“Il faut bien distinguer ici la pesanteur d'un corps d'avec son poids … La pesanteur dans un grand corps, n'est pas plus grande que dans un petit. Il n'en estpas ainsi du poids; il dépend non-seulement de la pesanteur, mais encore de la masse des corps…il est le produit de la pesanteur par la masse”(p. 155). Subsequently, he lays down the distinction between pesanteur and gravite which Clairaut adopted; but universally the English gravity has been used as synonymous with the French pesanteur. Airy, “Gravitation,” p. 3: “To take the ordinary force of gravity for an instance, we might measure it by the pressure which is produced on the hand…or by the number of inches through which the lump of lead would fall in a second of time … But there is this difference between the two measures; if we adopted the first…we should find a different measure by the use of every different piece of lead; whereas if we adopt the second … we shall get the same measure for gravity whatever body we suppose subject to its influence.” Here the broad distinction between “weight” and “gravity” is clearly laid down; the one is the “impressed force” on the falling body, the other its “accelerative effect” (Thomson and Tait, “Treatise on Nat. Phil.,” 217–219), or the more familiar “moving force” and “accelerating force.” In the “Treatise” the former is called the “force of gravity on the mass of a body,” 220; but “gravity” alone seems clearly enough defined as acceleration, by the words “According to this formula, therefore, polar gravity will be g = 32.088 × 1.005133 = 32.2527.”

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