On the Progress of Science as Exemplified in the Art of Weighing and Measuring: Being the Presidential Address Delivered Before the Washington ... Society, December 10, 1887 (Classic Reprint) - Softcover

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Excerpt from On the Progress of Science as Exemplified in the Art of Weighing and Measuring<br/><br/>Scientific men have long agreed that these requirements are best fulfilled by adopting as the fundamental units, a definite length, a definite mass, and a definite interval of time. Length is an element which can be very accurately measured and copied, but it must be defined by reference to some concrete material standard, as for example, a bar of metal, and as all substances expand and contract with changes of temperature, it is necessary to state the temperature at which the standard is correct. A standard of mass, consisting of a piece of platinum, quartz, or other material not easily affected by atmospheric in?uences, probably fulfills the conditions set forth above better than any other kind of magnitude. Its comparison with other bodies of approximately equal mass is effected by weigh ing, and as that is among the most exact of all laboratory operations, very accurate copies of the standard can be made, and they can be carried from place to place with little risk of injury. Time is also an element which can be measured with extreme precision. The immediate instruments of measurement are clocks and chronometers, but their running is checked by astronomical observations and the ultimate standard is the rotation of the earth itself.

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