de, gripping wheel is required in
front to carry the machine forward and to turn it on reaching the end
of the furrow. The wire-wound drum is actuated by a spring which tends
to keep it constantly wound up, and when the plough has turned and is
heading again towards the cable at the side of the field, this drum
automatically winds up the wire. So also when each pair of furrows has
been completed, the supply-wire is automatically shifted along upon
the fixed cable to a position suitable for the next pair.

Not only in the working, but also in the manuring, of the soil the
electric current will play an important part in the revolution in
agriculture. The fixing of the nitrogen from the atmosphere in order
to form nitrates available as manure depends, from the physical point
of view, upon the creation of a sufficient heat to set fire to it. The
economic bearings of this fact upon the future of agriculture,
especially in its relation to wheat-growing, seemed so important to
Sir William Crookes that he made the subject the principal topic of
his Presidential Address before the British Association in 1898.

The feasibility of the electrical mode of fixing atmospheric nitrogen
for plant-food has been demonstrated by eminent electricians, the
famous Hungarian inventor, Nikola Tesla, being among the foremost. The
electric furnace is just as readily applicable for forcing the
combination of an intractable element, such as nitrogen, with other
materials suitable for forming a manurial base, as it is for making
calcium carbide by bringing about the union of two such unsociable
constituents as lime and carbon.

Cheap power is, in this view, the great essential for economically
enriching the soil, as well as for turning it over and preparing it
for the reception of seed. Nor is the fact a matter of slight
importance that this power is specially demanded for the production of
an electric current for heating purposes, because the transmission of
such a current over long distances to the places at which the manurial
product is required will save the cost of much transport of heavy
material.

The agricultural chemist and the microbiologist of the latter end of
the nineteenth century have laid considerable stress upon the
prospects of using the minute organisms which attach themselves to the
roots of some plants--particularly those of the leguminaceae--as the
means of fixing the nitrogen of the atmosphere, and rendering it
available