"Nothing," he says, "can be more
evident than that the genial heat of the soil, particularly in spring,
must be of the highest importance to the rising plant; ... so that the
temperature of the surface, when bare and exposed to the rays of the
sun, affords at least one indication of the degree of the fertility."

Again he says: "The power of soils to absorb water from air is much
connected with fertility.... I have compared the absorbent powers of
many soils, with respect to atmospheric moisture, and I have always
found it greatest in the most fertile soils; so that it affords one
method of judging of the productiveness of land."

Where he erred was in overestimating the functions of the mechanical
properties of a soil, and in considering fertility to be due to them
alone.

During the next thirty years or so, little progress seems to have been
made in the way of fresh experimentation.

_Boussingault._

In 1834, Boussingault,[11] the most distinguished French agricultural
chemist of the century, began that series of brilliant chemico-agricultural
experiments on his estate at Bechelbronn, in Alsace, the results of which
have added so much to agricultural science. It was the first instance of
the combination of "science with practice," of the institution of a
laboratory on a farm; a combination peculiarly fitted to promote the
interests of agricultural science, and an example which has been since
followed with such magnificent results in the case of Sir John Lawes's
famous Rothamsted Experiment Station, and other less known research
stations.

Boussingault's first paper appeared in 1836, and was entitled, "The
amount of nitrogen in different kinds of foods, and on the equal value
of foods founded on these data."

In the year following other papers were published on such subjects as
the amount of gluten in different kinds of wheat; on the meteorological
considerations of how far various agricultural operations--such as
extensive clearings of wood, the draining of large swamps,
&c.--influence of climate on a country; and on experiments on the
culture of the vine.

Boussingault was the first observer to study the scientific principles
underlying the system of _rotation of crops_. In 1838 he published
the results of some very elaborate experiments he had carried out on
this subject. He also was the first chemist to carry out elaborate
experiments with a view to deciding the question of the assimilation by
plants