Page:Handbook of Meteorology.djvu/26

the molecular weight of any gas may be determined by comparing its weight with that of an equal volume of hydrogen. This is known as Avogadro’s law.

If a volume of gas be heated from 32° to 459° F^[1] (0° to 273° C) its volume will be doubled.^[1] That is, equal volumes of gases expand equally with the same increase of temperature.

If a given volume of gas—say 1 cubic foot of oxygen—be introduced within a container, its pressure or tension noted, the same volume of another gas having the same tension may be introduced without an increase of tension of the mixture. Thus 1 volume of oxygen added to I volume of nitrogen will make but 1 volume of the mixture, having the same tension as each of the two gases. That is, one gas is practically a vacuum for another. This property has its limitations; when several other gases are introduced within the container a noticeable increase of the tension of the mixture takes place.

Inasmuch as the science of meteorology is chiefly a study of the air, a mixture of gases differing in their specific properties, a clear exposition of these general properties is necessary to an understanding thereof—more especially to the solving of the problems of weather, climate, and habitability.

Gravity is a property of matter that exists apparently throughout the known universe. The apparent fact that matter in masses attracts all other matter in masses is practically all that is known of the essence of it. The whirling of the sun and the planets about a common center of gravity balances the attraction that otherwise would bring them together. More exactly stated, planetary bodies tend to move in straight lines; gravity tends to draw them to a common center; the result is orbital movement. These complex movements and forces have a great and very measureable influence on the movements of the sea and the air.

It is convenient to note the density—practically the “weight”

1. This may be expressed by the formula

   $V'=V[i+k(t'-t)]$,

   where $V$ is the given volume; $V'$ the volume sought; $t$ the given temperature; $t'$ the temperature of the volume sought; and $k$, 0.00367. This is known as Boyle’s law, and also as Mariotte’s law. It is true at high temperatures, but not exact at ordinary temperatures.