72 
ing that their heating effect 1s usually greater than those of the 
visible spectrum. 
The laws of growth or StL are the laws of physics and mechan- 
ics and chemistry as applied to living cells. The changes that go 
on slowly in the plant are not the same as would go on rapidly in 
large masses of the same chemicals when treated as in the ordinary 
chemical laboratory. In the plant small masses are confined within 
the transparent walls of the cells until that subtile influence which 
we call radiation can do its work in bringing about new combinations 
of the atoms. It matters not whether we consider the radiation as 
an orthogonal vibration, as in light, or a.promiscuous interpenetration 
of the molecules, as in heat, or a radial vibration, as in the waves 
of sound; whatever view we take of it, or whatever the details may 
be, even if it be a rythmic breaking up and re-formation of the mole- 
cules, the general characteristic of radiation is an extremely rapid 
motion along the molecules and atoms of matter. Therefore, by 
radiation we understand energy or momentum in the minute atoms 
that go to make up the molecules and the masses that we deal with; 
this implies that work is done by one atom upon its neighbor, which 
work, according to its style, we call hght, heat, evaporation, ete. 
Assimilation and transpiration are among the forms of work in the 
growth of the plant that are due to the molecular energy contained 
in sunshine, and it is essential to progress in agriculture that there 
be kept a continuous register of the intensity and nature of the solar 
radiations that reach the plant. But this is a difficult problem, whose 
satisfactory solution has not yet been attained, although the work 
of Violle, Bunsen and Roscoe, Marie Davy, Marchand, Langley, Row- 
land, Hutchins, and many others have marked out the methods which 
seem most promising. 
ANNUAL DISTRIBUTION OF SUNSHINE. 
Humboldt (1845), in his chapter on “ Climate,” after comparing 
the climates and fruits of Europe, says: 
These comparisons demonstrate how important.is the diversity of 
the distribution of heat throughout the different seasons of the year 
for the same mean annual temperature, as far as concerns vegetation 
and the culture of the fields and orchards, and as well as regards our 
own well-being as a consequence of these conditions. 
The lines which I call isochimenal and isotheral (lines of equal tem- 
perature for winter and summer) are not parallel to the isothermal 
lines (lines of equal annual temperature) in those countries where— 
notwithstanding the myrtle grows wild in its natural state, and where 
no snow falls during the winter—the temperature of summer and fall 
scarcely suffices to bring apples to full maturity. If to give a potable 
wine the vine shuns the islands and nearly all sea coasts, even those 
of the west, the causé is not only in the moderate heat of summer upon 
the seashore, a circumstance which is shown by thermometers exposed 
