36 



AGRICULTURAL ENGINEERING 



Fig. 21. 



area. It is to be noted that if a point within is taken as 



the apex of all the angles, it would 

 be necessary to measure, either all 

 three sides of each separate tri- 

 angle, or one side of each as a base, 

 and the altitude. 



Second Method: (Figs. 22 and 

 23.) The area of a many-sided 

 figure may be obtained by dividing 

 the field into parallelograms formed 

 by dropping a perpendicular from 

 each corner to a base line projected either across the field or 



on one side. It is to be 

 noted that all parallelo- 

 grams which are entirely 

 outside of the field are 

 negative areas, and their 

 sum should be subtracted 

 from the sum of those 

 having a part of their area inside 

 of the field. 



Figures With Irregular 

 Sides. First Method: The area 

 of a field with an irregular side 

 like that formed by a stream 

 may be obtained by considering 

 the irregular side to be formed 

 of short straight lines, and 

 measuring offsets, or per- 

 pendiculars erected from 

 a base line to points in this 

 broken line so as to form 



Fig. 23. 



Fig. 24. 



trapezoids, whose areas are easily found. 



