64 ELECTRICITY IN AGRICULTURE 
is under electrical treatment (experimental field), the other 
serving as the control field, we have to observe the following 
points :— 
(@) CHOICE OF FIELD, 
The qualities of the soi] must, as far as possible, be the 
same throughout the whole field—of the same composition, 
the same humidity, the same fertility, and of about the 
same height over a common level. The field must, 
further, be in the same way exposed to the sun, so that 
no shadow at all (@g., from growing trees) falls upon it. 
We will suppose that the experiments are to be made on 
six kinds of plants, and we then divide the field into 
squares, as shown in Fig. 8. 
E,| E2 Cy{C2 
E2| E; C2| Cy 
E,| E2 C1} C2 
Es|Eaj | Ca|Ca 
Ea| Es Ca} Cg 
Es| Es C3| C4 
Es| Ee Cs5|Ce 
E,| Es Ce| Cs 
Es|Eg| |Cs|Coe 
Fie. 8, 
The side of every square is 5 m*, making the area 
25 sq.m. When the experiments are made in a garden 
the squares can be arranged in two beds or layers, with 
a pathway between them. Such paths. must be made 
between the ranges of squares. In Fig. 8 the squares 
marked E,, E,, &c., represent experimental fields, and the 
squares marked C,, Cy, &c., the corresponding control 
fields. Between the two ranges of fields is left a space 
of 5 m., which can be sown with any sort of plant, but 
must be out of consideration so far as the experiment 
is concerned. 
