MEASUREMENTS 



331 



Doubtless the idea of the co-efficient of traction, already defined 

 ( 39) is more useful. It has been found in normal conditions : 



NATURE OF BODY IN SLIDING CONTACT CO-EFFICIENT OF 



TRACTION 



Iron wheels on iron rails 0-005 



or tyres on main roads 0-030 



The same on paving stone 0-015 



The same on a stony road 0-040 



non-stony road 0-068 



257. Table of Sines and Tangents. It will be recalled that the 

 cosine of an angle is equal to the sine of the complemental angle 

 (two angles whose sum equals 90 are said to be complementary; 

 and that 



tan a = 



sin a 

 cos a 



