In the tropical regions, where the days and nights vary little in
length, the temperature is nearly uniform throughout the year; while the
increasing inequality of day and night towards the Poles, causes an
increasing difference between the summer and the winter temperature.
Again, the length of the day, in the summer of high latitudes,
compensates for the diminished intensity of the Sun’s influence; so that
the temperature, in the hottest part of the day, may equal, or even
exceed, that within the tropics. A summer day in Labrador or Petrograd
may be as warm as one under the Equator; but in the former latitudes
there are only a few days of extreme heat in the year, while with
increasing nearness to the Equator the number of warm days constantly
increases.