715. Why does it vary more in the winter than in the summer?
Because the temperature of our climate differs more from the temperature of the torrid zones in the winter than it does in the summer, and the inequalities of temperature cause frequent changes in the degree of prevailing heat.
The same remarks (714, 715,) apply to the barometer.
CHAPTER XXXIV.
Sound is an impression produced upon the ear by vibrations of the air.
717. What causes the air to vibrate and produce sounds?
The atoms of elastic bodies being caused to vibrate by the application of some kind of force, the vibrations of those atoms are imparted to the air, and sound is produced.
718. How do we know that sounds are produced by the vibrations of the air, induced by the vibrations of the atoms of bodies?