MEASUREMENTS 



23 



Comparison of Wire Gauges — Continued 



No. 



9 

 10. 



11 . 



12. 



13 



14 



15 

 16 



17 



18, 



No. 



3i- 



32. 



33- 



34- 



35. 



36. 



37 



38. 



39 

 40 



Time. The unit of time is determined by the average 

 length of time between two successive passages of the sun 

 across the observer's meridian, known as the mean solar day, 

 consisting of 24 hours, each hour subdivided into 60 minutes 

 and each minute into 60 seconds. 



Temperature. The degree of heat or cold is measured by 

 a thermometer. The Fahrenheit (P.) is used for ordinary 

 work and the centigrade (C.) for scientific purposes. They 

 compare as follows : 

 32< 



•°F.=o°C. 



NORTH 

 POLE 



2I2°F. = IOO°C. 



Fahrenheit temperature = 



(% centigrade) +32 

 Centigrade temperature = 



(% Fahrenheit)- 32 ° 



Direction. Direction is expressed 

 by the use of the terms north and 

 east and their opposites south and 

 west. North is a fixed point near 

 the pole or North Star. A north 

 line, or a meridian, is a line passing 

 from the observer to the north point. 

 Since persons in different parts of 

 the earth's surface looking north are observing the same 

 point, north lines are not parallel, but are converging and 



Fig. 6. Showing the con- 

 vergence of the meridians 

 or north lines 



