24 



MENSURATION AND SURVEYING 



By figure** — 

 Measure off perpendiculars BC, AD ranging D in line 

 with OC. 

 OA OB 



AD == BC ;0A X BC = AD X(OA + AB)=ADX0A 

 + ADXAB ; ,\ OA(BC-AD) - AD X AB or OA = 

 AD X AB , 

 BC • - AD 



By figure 2 — 



Measure AB at right angles to AO and bisect AB at C. 

 Set off BD at right angles to AB until at D, C hides O. 

 Then AO = BD. 

 By figure 3 — 



Set off AC at right angles to AD and CB at right 

 angles to CO. 



Then OA X AB = AC 3 . 



AC 3 



Therefore OA = -Tg- 



B ;/ figure 4 — 



Fix any line AD and bisect it at F. 



Make BF = FC. Produce CD until at E. F hides O. 



Then AO = DE. 



Measurements of heights. 



Fix two rods AC, BD, of unequal height vertically as 

 shown so that C, D and T are in one line. Measure AB and 

 BH. 



mv TF DE TF DE 



Then FC = EC "AH^ AB ; 



TF 



DE X AH 

 AB 



