APPENDIX I 



SOME IMPORTANT INSTRUMENTS 



437. Weights and Measures. Standard masses called "weights " 

 are used in a balance in order to find the mass of any body of con- 

 venient size by weighing it, that is by finding how many of the 

 standard masses are attracted by the Earth with the same force as 

 the body of unknown mass is attracted. The standard masses may 

 be of any size or form, provided they can be easily 'obtained, and 

 new ones exactly equal to them made if the originals be lost. 

 Grains of seed were once used for this purpose, but now the standards 

 are always made of dense metal of a kind which does not alter in 

 the air. When a standard is once accepted it does not matter how 

 it originated, as copies are always made by actual weighing. The 

 British unit mass or pound avoirdupois is divided into 7000 grains 

 or 1 6 ounces, and 2240 pounds are called a ton. In the United 

 States the same unit pound is used, but 2000 of them are called a 

 ton. In English-speaking countries the way in which masses are 

 calculated is very contradictory and puzzling ; but almost all other 

 civilised nations employ a uniform system called the metric, the 

 unit mass of which is the kilogramme (equal to about 2^ Ibs.) 

 divided into 1000 grammes, and the gramme is similarly divided 

 into 10 decigrammes, or 100 centigrammes, or 1000 milligrammes. 

 These standards of mass are used by scientific men in every country, 

 although the results have often to be translated into pounds and 

 grains to make them popularly intelligible. The unit of length 

 amongst English-speaking people is the yard, divided into 3 feet 

 of 12 inches each, and 1760 yards are called a mile, although the sea- 

 mile or mean minute of latitude contains rather more than 2000 yards. 

 Measures on the metric system are like the weights subdivided 



