Abstract
IF Mr. Cumming's definition of specific gravity be accepted, the confusion, already serious enough, in the minds of beginners in physics between mass and weight will be much increased. Surely the best and clearest definitions of density and specific gravity are those given in Glazebrook and Shaw's “Practical Physics,” p. 105. These make density a quantity having dimensions in mass and space, and specific gravity a pure number. There are many advantages in defining specific gravity as a ratio, and not the least among them is that the numbers in tables of specific gravities are independent of any system of units, while in a table of quantities having dimensions the numbers given depend on the system of units used. Thus the density of platinum would have to be given in an English table as 1343.75 pounds, or in a metrical table as 21.5 grammes. Again we should lose the very useful analogies between the definitions of density and thermal capacity and specific gravity and specific heat, to which I drew attention in a letter to NATURE, vol. xxxiii. p. 391.
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ELDER, H. Density and Specific Gravity. Nature 38, 55 (1888). https://doi.org/10.1038/038055a0
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DOI: https://doi.org/10.1038/038055a0
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