Metric Act of 1866

The Metric Act of 1866, also known as the Kasson Act, is a piece of United States legislation that legally protected use of the metric system in commerce from lawsuit, and provided an official conversion table from U.S. customary units.

Congressman John A. Kasson from Iowa, then Chairman of the House Committee on Coinage, Weights, and Measures, proposed the act in his report of the Committee on Coinage, Weights, and Measures:

The metric system is already used in some arts and trades in this country, and is especially adapted to the wants of others. Some of its measures are already manufactured at Bangor, in Maine, to meet an existing demand at home and abroad. The manufacturers of the well-known Fairbanks scales state: “For many years we have had a large export demand for our scales with French weights, and the demand and sale is constantly increasing.” Its minute and exact divisions specially adapt it to the use of chemists, aphothecaries, the finer operations of the artisan, and to all scientific objects. It has always been and is now used in the United States coast survey. Yet in some of the States, owing to the phraseology of their laws, it would be a direct violation of them to use it in the business transactions of the community. It is therefore very important to legalize its use, and give to the people, or that portion of them desiring it, the opportunity for its legal employment, while the knowledge of its characteristics will be thus diffused among men. Chambers of commerce, boards of trade, manufacturing associations, and other voluntary societies, and individuals, will be induced to consider and in their discretion to adopt its use. The interests of trade among a people so quick as ours to receive and adopt a useful novelty, will soon acquaint practical men with its convenience. When this is attained—a period, it is hoped, not distant—a further act of Congress can fix a date for its exclusive adoption as a legal system. At an earlier period it may be safely introduced into all public offices, and for government service.

In the schedule of equivalents provided in the bill, extreme scientific accuracy is not expressed. The reasons follow. The exact length of the meter in inches and the weight of the kilogram in grains can of necessity be determined only approximately. The most careful determinations of these quantities now possible are liable to minute corrections hereafter, as more numerous observations are made and better instruments are used. Instead, therefore, of aiming at an accuracy greater, perhaps, than is attainable, it is more expedient to consult the convenience of the people by using the simplest numbers possible in the schedule, and yet such as shall be in fact more nearly exact than can ever be demanded in the ordinary business of life. These numbers are to be used in schools, and in practical life millions of times as multipliers and divisors, and every unnecessary additional figure is justly objectionable.

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