m the
Gulf Stream is to us the most striking example.

[Sidenote: Effects of ocean streams.] The physical action of the
sun-rays in occasioning currents operates through the expansion of
water, of which warm portions ascend to the surface, colder portions
from beneath setting in to supply their place. These currents, both hot
and cold, are affected by the diurnal rotation of the earth, the action
being essentially the same as that for the winds. They exert so great an
influence as conveyers of heat that they disturb the ordinary climate
relation depending on the sun's position. In this way the Gulf Stream, a
river of hot water in a sea of cold, as soon as it spreads out on the
surface of the Atlantic in higher latitudes, liberates into the air the
heat it has brought from the torrid zone; and this, being borne by the
south-west wind, which blows in those localities for the greater part of
the year, to the westerly part of the European continent, raises by many
degrees the mean annual temperature, thus not only regulating the
distribution of animals and plants, but also influencing human life and
its pursuits, making places pleasant that would otherwise be inclement,
and even facilitating the progress of civilization. Whatever, therefore,
can affect the heat, the volume, the velocity, the direction of such a
stream, at once produces important consequences in the organic world.

[Sidenote: Physical and chemical relations of water.] The Alexandrian
school had attained correct ideas respecting the mechanical properties
of water as the type of liquids. This knowledge was, however, altogether
lost in Europe for many ages, and not regained until the time of
Stevinus and Galileo, who recovered correct views of the nature of
pressure, both vertical and oblique, and placed the sciences of
hydrostatics and hydrodynamics on exact foundations. The Florentine
academicians, from their experiments on water inclosed in a globe of
gold, concluded that it is incompressible, an error subsequently
corrected, and its compressibility measured. The different states in
which it occurs, as ice, water, steam, were shown to depend altogether
on the amount of latent heat it contains. Out of these investigations
originated the invention of the steam-engine, of which it may be said
that it has revolutionized the industry of the world. Soon after the
explanation of the cause of its three states followed the great
discovery that the opinion of past ag