Zoe ANNUAL REPORT SMITHSONIAN INSTITUTION, 1958 
Because of our dependence on events taking place in the air, almost 
everyone is an amateur meteorologist. Wherever two or more people 
are gathered together the first topic of conversation is the weather, and 
this was probably just as true in the time of Hammurabi or Amenhotep 
asitistoday. Professional weathermen are a new development, how- 
ever, and it has only been within the last few decades that we have 
begun to gain an understanding of the great interrelated mechanisms 
of the air and the oceans. 
THE SUN 
We know that the sun pours a flood of particles and visible and in- 
visible light into the top of our atmosphere. The amount of visible 
light appears to be nearly constant, but the intensity of ultraviolet and | 
X-rays and the number of particles vary by at least a hundredfold. 
The particles are chiefly electrons and protons. The average number 
of hydrogen nuclei entering our atmosphere is surprisingly large, per- 
haps a billion per square centimeter per second. During the geological 
lifetime of the earth, if all this hydrogen were combined with oxygen 
as water, it would correspond to a layer over the ocean about 20 meters 
thick. The energy carried to the earth by these particles from the sun 
during periods of sunspot activity may be as much as one-tenth of the 
total energy of sunlight. 
In addition to particles of ordinary hydrogen, there is new evidence 
that most of the tritium or radioactive hydrogen on earth also comes 
from the sun. It was formerly thought that all the tritium was pro- 
duced by cosmic rays bombarding nitrogen and oxygen molecules in 
the upper air, but recent calculations indicate that the amount present 
ig nearly ten times too large to be produced in this way. 
The marked variations in ultraviolet radiation and in the number of 
particles coming from the sun cause large variations in the temperature 
and in the electrical and magnetic behavior of the upper atmosphere, 
because there is such a small amount of air at these high levels. Neither 
the majority of particles nor the ultraviolet rays penetrate very deeply, 
however, and it is not clear whether the variations in the amounts 
coming from the sun have appreciable effects near the earth’s surface. 
Visible light is the dominant form of solar energy entering the lower 
atmosphere. Part of this light is reflected back to space, chiefly from 
the surface of clouds, snow, and ice. Most of it is absorbed in the 
atmosphere and the sea, from which it is ultimately re-radiated as 
infrared radiation. 
In this respect, the atmosphere behaves much like the glass in a 
greenhouse. It easily transmits visible hight but is rather opaque 
to the infrared or heat radiation coming from the ground and the 
sea surface. Just as in a greenhouse, the air temperature must be 
considerably warmer than it would be in the absence of materials 
