68 ELECTRICITY IN AGRICULTURE 
to put the spheres of the discharger so near that sparks are 
intermittently passing between them, These sparks are 
very small, but they will keep the machine charged; a 
Leyden (Lane)* jar in the conductor to earth will have the 
same effect. 
Remarks.—During the experiments with this installation 
attention must always be directed to the insulation of the 
wire net and the charging of the machine. 
The insulators must be carefully observed every day, 
because spiders make their webs over from the wire net to 
the posts. This web must be cleared away. 
When the electric machine is kept in a dry room, it will 
be charged at the first turns. In the summer it sometimes 
happens that the air in the room is colder than that outside. 
In this case a condensation of watery vapour begins within 
the machine, and its insulation is destroyed. (This has 
not hitherto been observed, because the older machines 
have never been used for continuous work, and have always 
been kept in an ordinary room with dry air.) The best 
course is, therefore, to put the machine, together with the 
motor, in a small room on an upper floor (about 2 square 
metres in area), provided with a small fireplace with the 
fire laid ready to be lighted, or a small heating apparatus 
with source of heat outside, care being taken that the tem- 
perature inside the room is always two or three degrees 
higher than that outside. 
The best method to observe, with regard to the supply 
of the electric current, is to construct, as it were, a central 
supply station, to branch out conductors 5 km. on all sides 
around it, and to sell the electricity as an ordinary article of 
commerce. In this way the cost of current will be ascer- 
tainable, and this is most desirable from all points of view. 
COST OF THE INSTALLATION. 
The cost of an installation for the application of elec- 
tricity to growing plants on a field of an area of 10 hectares 
* A Leyden jar transformed into a Lane jar is a jar with which the length 
and the number of sparks can be measured. 
