EXCAVATING MACHINERY USED IN LAND DRAINAGE. 
25 
SELECTION OF SCRAPER EXCAVATOR. 
In selecting a scraper excavator the purchaser, in addition to 
choosing the most desirable kind of power and the best means of 
moving over the ground in his particular case, must determine the 
length of boom best suited to his needs. 
Figure 2 is a diagram showing the relation between the length and 
angle of elevation of boom and the effective reach of machine. In 
this diagram all distances are referred to the heel of the boom. If it 
is desired to refer horizontal distances to the center of the machine, 
the correction A must of course be added; this distance varies with 
the different makes of machine. The distance, B, of the heel of the 
boom above the ground, likewise varies slightly in different machines. 
_L REACH OF BOOM IN FEET FROM CENTER OF BOOM LUG AT VARIOUS ANGLES. 
a — ■ — A— — *. To This Distance add 'A" nhcn Distance from Center of Machine is required. 
Yig. 2.— Diagram of scraper excavator, showing relation between the length and elevation of boom and 
the effective reach of machine. 
To determine the maximum clearance of the bucket above the ground 
for different lengths and positions of boom, the distance B must be 
added to the vertical heights given on the right-hand margin of the 
diagram; and from this sum must be subtracted the distance C, which 
will depend entirely upon the type of bucket used. Thus, for a 
70-foot boom elevated at an angle of 35°, the horizontal distance 
from the center of machine to the bucket would be 57 + A; and at 
that position of the boom the bucket would just clear a waste bank of 
a height 40 + B-C. 
THE DRY-LAND DIPPER EXCAVATOR. 
Excavating machines employing the same digging principle as used 
on the floating dipper dredge, but moving on land, either over or in 
