spread out, so as to leave only the extreme northern and southern points of the continent outside their limits. A third narrowing is to be found at the western side of the irregular land mass formed by Australia, the Malay Peninsula, and the intervening islands, but is much less marked, amounting to a few degrees only. The comparative coolness of the western sides of the great continental masses is due to the existence of northerly currents of cold water coming from the frozen seas of the south pole, which wash the western coasts, while along the east coast there sets a current of warm water coming from the Equator. The principal factor in the determination of climatic characteristics is the fact that while the land heats and cools with great rapidity, the sea does so more slowly, but holds the heat better. This is due to two circumstances. In the first place, it requires more heat to warm a given weight of water than an equivalent mass of the various substances which constitute the land. In the second place, while both are alike bad conductors of heat; water, being a fluid, is mobile, and in the colder parts of the globe where the surface is colder than the intermediate depths, convection comes into play, apart from which the least movement at the surface is sufficient to distribute the heat gained from the sun to a greater depth than is possible in the case of the solid constituents of the earth’s crust. The second great determinant of climate is the fact that the temperature of the air is determined for the most part by that of the surfaces with which it is brought into contact, rather than by the passage of the sun’s rays through it, as is well shown in the arctic air temperatures of great elevations in tropical latitudes. From this it follows that the atmosphere is mainly heated by the sun’s rays indirectly, from below where it is in contact with the directly heated, solid and liquid surface of the globe.