

CHAPTER I 



MEASUREMENT OF LENGTH 



1 . Exact measurement is the foundation of science, 

 hence our first concern will be to consider how measure- 

 ments are usually stated, and to follow this by the 

 description of some simple measuring instruments and 

 how to use them. 



In speaking of any measurement we use two words 

 a name and a number. The name is that of some 

 x chosen measurement with which the other measurement 

 is compared, and is termed the " unit " measure. The 

 number tells us how many times the actual measure- 

 ment in question contains the unit measure. Let us 

 suppose the measurement we wish to make is that of 

 the length of the edge of a table. We may use as our 

 unit of length that of a page of this book. By com- 

 paring this length in some suitable manner with that 

 of the table-edge, we may find that the table is eight 

 times as long as the book. We express this by the 

 statement that the edge of the table is eight page- 

 lengths long. The unit measure is here a " page- 

 length", and the number "eight" is the number of 

 times the length of the table-edge contains the unit. 

 Should another table of the same length be required, 

 however, it would greatly surprise a cabinet-maker to 

 be asked for a table eight page-lengths long. He 

 would probably ask " How long is the page that you 



H. D. S. 1 



