146 TECHNOLOGY. 
sufficient fall or descent to carry off the water which collects in them. The 
operation commences with the construction of a main drain through the 
lowest portion of the field, to receive and carry off the contributions of the 
minor drains. This main drain is best left open, and in general should be 
at least three feet wide at the bottom, and three feet deep; from this radiate 
over the whole surface of the ground to be drained, the under-ground 
branches, which, having been dug to the requisite depth, are filled with 
stones, bushes, straw, reeds, or similar substances, as they may be at 
hand. 7 
If stones be made use of, care should be taken that none are so large as 
to fill alone the bottom of the drain; in general the stones should lie hol- 
low, so as to permit the passage of the water, and not dam it up at any one 
point. Pl. 30, jig. 29, is not an unusual arrangement, the drain being 
covered first with a layer of straw, rushes, &c., then with the soil. Where 
reeds and straw are made use of, jig. 30 shows a common arrangement. 
When the drain itself is filled with these materials, there should be a space 
above of at least one foot, which is to be filled with the surface soil; this 
should be heaped over the drain, that as the ground gradually consolidates 
it may not sink below the general surface. 
In England, where draining is extensively practised, the plough is made 
use of in opening the drains, which materially lessens the cost of excavation. 
The following tools are also made use of in England: The drain shovel (pi. 
30, figs. 10, 11, and 12), and drain hoes of various forms and sizes (jigs. 8 and 
9). The earth-borer is often made use of to advantage to ascertain the 
nature of the ground beneath the surface, as the labor of draining may often 
be reduced by finding a stratum of gravel beneath, into which the surface 
water may be conducted. For minor depths, the auger shown in jig. 15 is 
quite sufficient. When a greater depth of auger is required, an instrument, 
shown in jig. 16, is made use of. /%g. 17 is the shaft of the auger ; jig. 18, 
the handle; jig. 19, the guide for directing the rod of the auger when a con- 
siderable depth is to be attained. 
Whilst we are speaking of English operations, we will take occasion to 
mention a few instruments in use in England for cultivating and hoeing 
vegetable crops. Pl. 80, jig. 14, is a hoe used to thin out plants where 
they stand too thick; jig. 13 is a double-pointed hoe, of Portuguese 
origin, and serves to cultivate on both sides of a plant. The treble-pointed 
hoe (fig. 22) is for working between the rows of garden vegetables ; jigs. 23 
and 21 are other forms of hoe used for the same purpose ; p/. 30, jig. 20, is an 
instrument for cutting and grubbing up roots of trees and small shrubs. 
F, Double Crops. 
Not unconnected with the present article is the subject of double crops. 
We shall limit ourselves, however, to the consideration of a method prac- 
tised with success in Austria, for obtaining a crop of small grain and a crop 
of roots from the same ground each year. 
The field (pl. 30, jig. 1) is ploughed and harrowed in the usual manner, 
and planted with small grain, wheat, rye, or oats, in rows two feet apart; 
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