THE METRIC SYSTEM. .321 



What applies to currency units applies also to units of length, area, 

 volume and weight. • A simple rational system of such measures must, 

 as is generally admitted, be a decimal system. In this way large and 

 small units may be related like the dollars, cents and mills of our cur- 

 rency. Such a system could not have been introduced until arith- 

 metical science had reached a sufficiently general development, say, at 

 the opening of the eighteenth century. 



Commerce and labor must have demanded systems of weight and 

 measures as far back as we have knowledge of the doings of nations. 

 It is no wonder that these systems should have been crude, labor- 

 absorbing and unscientific. No disparagement can be imputed to the 

 English-speaking nations for inheriting from remote ancestry a crude 

 system of weights and measures. Criticism of such nations can surely 

 only be fairly laid at their doors when, seeing that their neighbors 

 have a better modern system, up to date and practical, they remain 

 supine and make no attempt to join the ranks of international progress. 



In British and American measures of length we have the following 

 units, all taught in the schools and all used more or less — league, 

 statute mile, furlong, engineer's chain, surveyor's chain, rod-pole-or- 

 perch, yard, foot, engineer's link, span, surveyor's link, hand, inch 

 and line. These numerous units involve more than a hundred cross- 

 connecting ratios, many of which would, it is true, be very 

 seldom called for. Even, however, if we confine ourselves to mile, 

 yard, foot and inch, we have the following six connecting ratios: 

 3, 12, 36, 1,760, 5,280, 63,360. 



In the metric system there is the meter, about ten per cent, longer 

 than the yard, and its decimal derivatives, all evaluated at a glance by 

 a shift of the decimal point. In English speaking countries, roads are 

 measured in miles and furlongs, short distances in yards, houses or 

 ships in feet, horses in hands and small objects in inches. These ex- 

 pressions are not exchangeable or translatable without more or less 

 mental effort. In the metric system, roads are measured in kilometers 

 and hectometers, short distances in meters or dekameters, small ob- 

 jects in centimeters or millimeters and microscopic objects in micro- 

 meters or microns. Taking the length of a good-sized bacterium as 

 one micron, it is immediately evident to the mind that a million such 

 bacteria would fit into a meter, and one thousand million into a kilo- 

 meter. If, however, we take the size of the bacterium as a certain 

 small fraction of an inch, it takes time and considerable mental effort 

 to find the corresponding relation of dimensions. 



The same difficulty exists with units of area in the customary 

 system. We have the square inch, square foot, square yard, square 

 rod, rood, acre, square mile and township. All these units are used, 

 although some are used only by surveyors. These involve 45 connect- 



