Letter | Published:

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

Naturevolume 13page466 (1876) | Download Citation



THE relations between weight and mass, gravity and acceleration, are so well defined in all good treatises on dynamics, that it appears superfluous to dwell on these questions. But as it has been stated by Prof. Barrett, vol. xiii., p. 385, that the C. G. S. system of units has been introduced into the course of Mechanics in this College, I may be permitted to say that the system actually employed is not that referred to by your correspondent. I generally employ the kilogramme, metre, and second, and sometimes the foot, pound, and second, to measure a dynam or unit of force. The dynamometers alluded to as about to be exhibited at the Loan Exhibition of Scientific Instruments at South Kensington are suitable to the former system, and I use them for the measurement of dynams in kilogrammetres. One of these dynamometers is graduated for every 200 grammes up to 100 kilogrammes, the other for every 100 grammes up to 10 kilogrammes, and they cannot be depended on for results within the tenth of a kilogramme. Spring dynamometers, though suitable for the large units employed in mechanics, are totally unfit for measuring units on the C. G. S. system. I concur with Prof. Everett, in his book on this system, when he says:—“A spring balance, it is true, gives a direct measurement of force, but its indications are too rough for purposes of accuracy” (p. 8). Spring dynamometers are therefore unsuited to a system where the units are measured by 1/981 of a gramme, or about 1/63 of a grain, as in the C. G. S. system.

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  1. Royal College of Science for Ireland, Dublin



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