en. TV MASS AND ITS MEASUREMENT 45 



But this ungainly system of units docs not exhaust the difficul- 

 ties of the British system of estimating masses, for if the mass 

 of a body composed of one of the precious metals, platinum, gold, 

 or silver, or of some precious stone, is to be expressed another 

 system known as " Troy Weight, " is used. Moreover, the 

 ounce in the last-named system is differently sub divided again 

 if the masses of drugs are being dealt with. 



Units of Mass in the Metric System. In the metric 

 system a name is given to the mass of pure water which will 

 r.ntct! i/ fill (i i-nliir << iif hnctre at a temperature of 4 C C. It is 

 called a gram. The same prefixes are used to express fractions 

 and multiples of a gram as have been used in the case of the 

 metre and litre. The kilogram is one thousand times greater than 

 one gram, and is the unit in use for ordinary purposes. Other 

 multiples are in common use, as the following table shows : 



J.O milligrams = 1 centigram. 



10 centigrams = 1 decigram. 



10 decigrams = 1 gram. 



10 grains = 1 dekagram. 



10 dekagrams = 1 hectogram. 



10 hectograms = 1 kilogram. 



10 kilograms = 1 myriagram. 



10 myriagrams = 1 quintal. 



10 quintals = 1 millier. 



Relation between British and Metric Units of Mass : 



Metric to British. 



1 decigram = 1 '5432 grains. 

 i 1 gram = 15 '4323 grains. 



1 dekagram = '3215 oz. Tr. 

 1 hectogram = 3'5274ozs. Av. 

 1 kilogram = 2 '2046 Ibs. Av. 



British to J/Wn'c. 



^1 grain = '648 decigram. 



1 oz. Tr. = = ' 3-1103 dekagrams. 



^ 1 ox. Av. = 2 '835 dekagrams. 

 i,l 11). Av. '4503 kilogram. 



Gravitation. It is a matter of everyday observation that 

 masses free to move gravitate, as we say, towards the earth ; or 



