Abstract
I.
WE cannot measure time in that sense in which we measure other things. Time has been very happily denned as the great independent variable of all change; and it is by watching matter in motion, which is the simplest form of change with which we are acquainted, that we estimate its progress. Thus, the motion of the earth around its axis furnishes us with that well-defined interval, the day; and the motion of pendulums (which swing against the earth's attraction) and of watch balances (which swing against the attraction of the particles of matter of which their springs are composed) furnish us with its subdivisions. I mention this at starting, because during our discussion, I want you perpetually to bear in mind that pendulums and watch balances are not mere appendages or terminations to the mechanism of time-measuring apparatus, but are themselves the true time-measurers; and in general, the question of accurately constructing such apparatus resolves itself into the problem of obtaining an uniform impulse-just such an impulse, neither more nor less, which shall exactly restore to the pendulum or watch balance that amount of motion, of which it has, during its preceding swing, been deprived, by the friction of its connections, and the resistance of the atmosphere.
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Principles of Time-Measuring Apparatus 1 . Nature 14, 529–531 (1876). https://doi.org/10.1038/014529a0
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DOI: https://doi.org/10.1038/014529a0