560 EVERYDAY SCIENCE 



therefore equal to the mass of a cubic centimeter of water at 

 the same temperature. The mass of a given body of water 

 can thus be immediately inferred from its volume. 



The unit of mass in the English system is the avoirdupois 

 pound. The ton of 2000 pounds is its chief multiple; its 

 submultiples are the ounce and the grain. The avoirdupois 

 pound is equal to 16 ounces and to 7000 grains. The " troy 

 pound of the mint " contains 5760 grains. In 1866 the mass 

 of the 5-cent nickel piece was legally fixed at 5 grams ; and 

 in 1873 that of the silver half dollar at 12.5 grams. One 

 gram is equal approximately to 15.432 grains. A kilogram 

 is very nearly 2.2 pounds. More exactly, one kilogram 

 equals 2.20462 pounds. 



All mail matter transported between the United States and the 

 fifty or more nations signing the International Postal Convention, 

 including Great Britain, is weighed and paid for entirely by metric 

 weight. The single rate upon international letters is applied to the 

 standard weight of 15 grams or fractional part of it. The Inter- 

 national Parcels Post limits packages to 5 kilograms; hence the 

 equivalent limit of 11 pounds. 



Common Units in the English System : 



1 ton (T.) = 2000 pounds (Ib.) 

 1 pound =16 ounces (oz.) 

 1 ounce = 437.5 grains (gr.) 



Common Units in the Metric System : 



1 kilogram (kg.) = 1000 grams (g.) 



1 gram = 1000 milligrams (mg.) 



The Unit of Time. The unit of time in universal use 

 in physics and by the people is the second. It is S6 1 00 

 of a mean solar dav. The number of seconds between 



