INTKODUCTOKY CHAPTER 



FRENCH AND ENGLISH SCIENTIFIC UNITS. 



IN the varied examinations into the qualities and properties of 

 matter with which Physical Science is especially concerned, 

 certain units of measurement are essential. And it is unfortunate 

 that in different countries these units are not the same. The Metric 

 or French system, however, is now so universally acknowledged to 

 be the best for scientific purposes, that the Editor by the advice of 

 eminent scientific friends has retained it in this work. Its retention 

 renders necessary a few words by way of introduction. 



One great advantage of the Metric System ever our own is that it 

 is a decimal system : thus, by the simplest decimal system of multi- 

 plication and division, we are enabled to perform with speed and 

 ease any calculations connected wtth it which may be necessary; 

 another is that the same prefixes are used for measures of length, 

 surface, capacity, and weight ; and, finally, these various measures are 

 related to each other in the simplest manner. 



Unit of Length. The English unit of length is the yard, the length 

 of which has been determined by means of a pendulum, vibrating 

 seconds in the latitude of London, in a vacuum, and at the level of 

 the sea. The length of such a pendulum is to be divided into 

 3,913,929 parts, and 3,600,000 of these parts are to constitute a yard- 

 The yard is divided into 36 inches, so that the length of the seconds 

 pendulum in London is 39'13929 inches. 



The French unit of length, called the metre (from per pew, I measure), 

 has been taken as being the ten-millionth part of the quadrant of a 



