Emily C. Allen, aged 11, of Portland, Me, for her question:

How many gases are there in the air?

We know of ten gases present in the air. At lower levels, all but one of these gases keep to the same proportions. Seven of the gases which make up our air are present in only very small quantities.

Nitrogen forms 78.3 percent of the air around us. It is inactive gas and serves as a sort of policeman, or buffer. It dilutes the oxygen and prevents it from being too active. Oxygen, so busy and necessary to living things, forms 20.90 percent of the air„ These two gases form 99.2 percent of the atmosphere.

The gas argon forms ,93 percent of the air. Carbon dioxide forms .03 percent, Five rare gases, found only in traces, form another .02 of the air around us. They are krypton, helium, hydrogen, neon and xenon.

Also present in the air is water vapor ‑ which is water in its gaseous state. It is not possible to give an all‑over account of the vapor present in the air. For it varies from time to time and from place to place.