1 62 The National Geographic Magazine 



there, and how much does the water 

 weigh? The answer is 123,456.789 liters, 

 weighing 123,456.789 kilograms. 



Now, supposing we forget for the mo- 

 ment that one liter of water contains one 

 thousand cubic centimeters and weighs 

 one kilogram, it is not necessary for us 

 to consult a work of reference. A mo- 

 ment's consideration of the elementary 

 propositions of the metric system will en- 

 able us to recover the knowledge for our- 

 selves by mere mental computation. We 

 cannot forget that one cubic centimeter 

 of water weighs one gram, for that fact 

 lies at the root of the relation of weight 

 to volume in the metrical system. We 

 cannot forget the equally elementary 

 proposition that a cube having a side of 

 10 centimeters has a volume of one liter, 

 for this lies at the root of the relation of 

 length to volume on the metrical system. 

 If we do not know these facts, we do not 

 know the metrical system at all. 



A cube having a side of 10 centimeters 

 has a volume of one liter ; then how many 

 cubic centimeters are there in a liter? 

 Picture to yourself a cube of the required 

 dimensions and mentally calculate the 

 cubical contents. It is 10 centimeters long, 

 10 centimeters wide, and 10 centimeters 

 deep. Multiply these dimensions to- 

 gether ; 10 times 10 is 100, and 10 times 

 100 is 1,000. Here we recover the for- 

 gotten fact that a liter contains 1,000 

 cubic centimeters. But one cubic centi- 

 meter of water weighs one gram; from 

 which it follows that 1,000 cubic centi- 

 meters (one liter) weigh 1,000 grams 

 (one kilogram). 1,000 is the figure 1 

 followed by 3 ciphers ; and this fact di- 

 rects us to shift the decimal point 3 places 

 to the left in order to convert cubic centi- 

 meters of water into liters of volume or 

 kilograms of weight. 



Contrast the amount of labor involved 

 in this simple process with that involved 

 in ascertaining from the number of cubic 

 inches of water the volume of water in 

 gallons and its weight in pounds. Noth- 

 ing, I think, can better illustrate the fact 



that the metric system is a labor-saving 

 device of the greatest importance and 

 value. 



It is safe to say that after the metric 

 system has been adopted by the United 

 States and our people have become ac- 

 customed to its use we would no more 

 dream of going back to the present sys- 

 tem of weights and measures than we 

 would think of carrying on the processes 

 of arithmetic through the medium of the 

 old Roman letters in place of the Arabic 

 numerals we now employ. 



the; experience of dr beei/s 

 laboratory 



The laborious nature of the calcula- 

 tions involved in the use of our ordinary 

 measures was forced upon my attention 

 a number of years ago by the fact that I 

 commenced to carry on in my laboratory 

 a series of experiments with man-lifting 

 kites — enormous structures, which had to 

 be made very light in proportion to their 

 supporting surfaces in order to carry a 

 man up into the air. These kites cost 

 several hundred dollars apiece to con- 

 struct; and it was therefore found ad- 

 visable, after repeated failures, to cal- 

 culate beforehand what the weight of a 

 proposed structure would be; and then 

 calculate, from the total amount of silk 

 employed and from the angle which the 

 oblique surfaces made with the horizon, 

 the amount of effective surface upon 

 which the wind would act (the projection 

 of the oblique surfaces on a horizontal 

 plane). From these figures the ratio of 

 weight to support surface for the whole 

 structure was ascertained and the fact de- 

 termined whether the proposed kite 

 would fly in a moderate wind — before 

 actually commencing its construction. 

 The calculations proved to be so labori- 

 ous that I found it simpler to translate 

 the proposed measurements into metrical 

 terms and then work out the solution on 

 the metrical plan. 



The translation of the ordinary meas- 

 urements into metrical terms, and vice 



