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Page:Popular Science Monthly Volume 49.djvu/201

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187
THE METRIC SYSTEM.

standing reproach and anomaly—a change for changing's sake. The change, if we make it, must be complete and thorough. And this is in the face of the fact that England is beyond all question the nation whose commercial relations, both internal and external, are the greatest in the world, and that the British system of measures is received and used, not only throughout the whole British Empire (for the Indian "Hath" or revenue standard is defined by law to be 18 British imperial inches), but throughout the whole North American continent, and (so far as the measure of length is concerned) also throughout the Russian Empire. . . . Taking commerce, population, and area of soil then into account, there would seem to be far better reason for our Continental neighbors to conform to our linear unit could it advance the same or a better a priori claim than for the move to come from our side. (I say nothing at present of decimalization.)

Sir John Herschel then argues that the 10,000,000th part of the quadrant of a meridian, which is the specified length of the metre, is, on the face of it, not a good unit of measure, inasmuch as it refers to a natural dimension not of the simplest kind, and he continues thus:—

Taking the polar axis of the earth as the best unit of dimension which the terrestrial spheroid affords (a better a priori unit than that of the metrical system), we have seen that it consists of 41,708,088 imperial feet which, reduced to inches, is 500,497,056 imperial inches. Now, this differs only by 2,944 inches, or by 82 yards, from 500,500,000 such inches, and this would be the whole error on a length of 8,000 miles which would arise from the adoption of this precise round number of inches for its length, or from making the inch, so defined, our fundamental unit of length.

After pointing out that the calculation required for correlating a dimension so stated with the earth's axis is a shorter one than that required for correlating such dimension with the quadrant of a meridian. Sir John Herschel argues that—

If we are to legislate at all on the subject, then the enactment ought to be to increase our present standard yard (and, of course, all its multiples and submultiples) by one precise thousandth part of their present lengths, and we should then be in possession of a system of linear measure the purest and most ideally perfect imaginable. The change, so far as relates to any practical transaction, commercial, engineering, or architectural, would be absolutely unfelt, as there is no contract for work even on the largest scale, and no question of ordinary mercantile profit or loss, in which one per mille in measure or in coin would create the smallest difficulty. Hitherto I have said nothing about our weights and measures of capacity. Now, as they stand at present, nothing can be more clumsy and awkward than the numerical connection between these and our unit of length.

And then, after pointing out the way in which the slight modification of the unit of linear measure described by him could be readily brought into such relation with the measures of capacity and weight as to regularize them, he goes on:—

And thus the change which would place our system of linear measure