Distances Measured
Many people hear of distances in thousands of yards—a usual measure of artillery distances—and have very little power of reducing them at once to miles. Now, four miles are ten yards for each mile above 7000 yards, whence the following rule: the number of thousands multiplied by 4 and divided by 7 give miles and sevenths for quotient and remainder, with only at the rate of ten yards to a mile in excess. Thus 12,000 yards is 48 7ths of a mile, or 6 miles and 6 7ths of a mile: not 70 yards too great. Again, people measure speed by miles per hour, the mile and the hour being too long for the judgment of distance and time. Take half as much again as the number of miles per hour, and you have the number of feet per second, too great by one in 30. Thus 16 miles an hour is 16 + 8, or 24 feet per second, too much by 24-30ths of a foot.—Athenæum, No. 1854.