What is Newton's original definition of mass.

The following is from the English translation of Newton's Principia by Andrew Motte.

"The quantity of matter is the measure of the same, arising from its density and bulk conjointly."

"Thus air of double density, in a double space, is quadruple in quantity; in a triple space, sextuple in quantity. The same thing is to be understood of snow, and fine dust or powders, that are condensed by compression or liquefaction, and of all bodies that are by any causes whatever differently condensed. I have no regard in this place to a medium, if any such there is, that freely pervades the interstices between the parts of bodies. It is this quantity that I mean hereafter everywhere under the name of body or mass. And the same is known by the weight of each body, for it is proportional to the weight, as I have found by experiment on pendulums, very accurately made, which shall be shown hereafter."

I once remember reading about Newton making pendulums of different material, lead, copper, others.. and doing some sort of experiments with them to show his:

"And the same is known by the weight of each body, for it is proportional to the weight".

I now cannot trace such passages in my recent downloaded copy of my Principia.

Can anyone point me to some sources to clear this point?


1 Answer 1


I have found the answer. The passages is in Book 3, Proposion VI, Theorem VI; page 394.

  • 1
    $\begingroup$ No! It is in DEFINITIONS, DEFINITION I of Principia $\endgroup$
    – user366648
    May 9, 2023 at 11:17

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