170 



Mr Galbraith on Trigonometrical 



Table III. To convert the Values of small Arcs derived from their Lengths 

 into those obtained from their Sines or Tangents. 

 A sin a = R" (arc a — sin a) to radius unity. 

 A tan a i= R" (tana — arc a) zz 2 a sin a nearly. 



This table gives the same results as the usual approximative rule ge- 

 nerally given to find degrees, minutes, and seconds, answering to the 

 log. sine or tangent of a very small arc, and is not perfectly accurate 

 above two or three degrees, beyond which such calculations should not 

 be carried. 



Table IV. To convert Feet on the earth's surface into Arcs when the com- 

 pression £ rZ gij. 



