86 
THE PHYSICAL GEOGRAPHY OF THE SEA. 
nearer the equator ill the winter and spring months than at any- 
other season. 
The southwest winds commence at this season to prevail as far 
down as the lower part of California. In winter and spring, the 
land in California is cooler than the sea air, and is quite cold 
enough to extract moisture from it. But in summer and autumn 
the land is the warmer, and can not condense the vapors of water 
held by the air. So the same cause which made it rain in Ore- 
gon now makes it rain in California. As the sun returns to the 
north, he brings the calm belt of Cancer and the northeast trades 
along with him ; and now, at places where, six months before, the 
southwest winds were the prevailing winds, the northeast trades 
are found to blow. This is the case in the latitude of California. 
The prevailing winds, then, instead of going from a warmer to a 
cooler climate, as before, are going the opposite way. Conse- 
quently, they can not, if they have the moisture in them to make 
rains of, precipitate it under such circumstances. 
131. Panama is in the region of equatorial calms. This belt 
of calms travels during the year, back and forth, over about 17° 
of latitude, coming farther north in the summer, where it tarries 
for several months, and then returns so as to reach its extreme 
southern latitude some time in March or April. Where these 
calms are it is always raining, and the chart shows that they hang 
over the latitude of Panama from June to November ; consequent- 
ly, from June to November is the rainy season at Panama. The 
rest of the year that place is in the region of the northeast trades, 
which, before they arrive there, have to cross the mountains of the 
isthmus, on the cool tops of which they deposit their moisture, 
and leave Panama rainless and pleasant until the sun returns north 
with the belt of equatorial calms after him. They then push the 
belt of northeast trades farther to the north, occupy a part of the, 
winter zone, and refresh that part of the earth with summer rains. 
This belt of calms moves over more than double of its breadth, 
and nearly the entire motion from south to north is accomplished 
generally in two months. May and June. 
132. Take the parallel of 4° north as an illustration : during 
these two months the entire belt of calms crosses this parallel, and 
then leaves it in the region of the southeast trades. During these 
two months it was pouring down rain on that parallel. After the 
