32 ELEMENTARY GENERAL SCIENCE CHAP. 



jar graduated into c. cm. The volume of the solid used, in 

 metric units, is shown by the rise of the water above its 

 original level. 



If the object is lighter than the liquid employed, a sinker made 

 of lead or iron should be employed. First find the volume of 

 the sinker as in Expt. 42 ; then take the sinker out of the water 

 and tie it with thread to the light object, and place them both 

 in the jar. The additional rise of level which takes place will 

 give the volume of the object itself. 



CHIEF POINTS OF CHAPTER II. 



Measurement of Length. In the British system the standard of 

 length is the yard. It may be denned as the length between two marks 

 on a platinum bar kept at the Exchequer Chambers, the bar being 

 at a certain fixed temperature when the measurement is made. The 

 yard is subdivided into feet and inches. The multiples of the yard 

 are given on p. 21. 



In the metric system the standard is the metre ; it may be defined 

 as the length, at a certain temperature, between two marks on a 

 platinum bar kept at Paris. It is equal to 39 '37079 inches. It is 

 subdivided into decimetres, centimetres and millimetres. The multiples 

 are the dekametre, hectometre and kilometre (p. 22). 



Measurement of Area. In measuring areas or space of two dimen- 

 sions, the same names are employed as when speaking of lengths 

 with the word square prefixed. We thus get such terms as square 

 foot and square decimetre. Since there are 12 linear inches in a 

 linear foot there will be 12 x 12= 144 square inches in a square foot. 

 The British and metric units of area are given on p. 25. 



Measurement of Volume. In measuring volumes, or space of three 

 dimensions, we employ, in the British system, such terms as cubic foot 

 and cubic yard. Since there are 12 linear inches in a linear foot 

 there will be 12 x 12 x 12= 1728 cubic inches in a cubic foot. 



In the metric system a special name is given to a cubic decimetre, 

 that is to the volume contained by a cube having a decimetre edge, 

 it is called a litre and is equal to about one and three-quarters 

 English pints. The names of the multiples and sub-multiples of the 

 litre are formed in the same way as in the case of the metre (p. 29). 



Relation between British and Metric Units in the cases of length, 

 area and volume are given in the course of the chapter and should 

 be carefully examined by the student. 



QUESTIONS ON CHAPTER II. 



1 . What is the necessity for units of length, area and volume ? 

 What is the unit of length in common use in this country and how 

 may it be defined ? 



2. What is the unit of length in the metric system ? What rela- 



