USE OF OCEANOGRAPHY—DEACON al 
the changes from year to year can be as much as 7.5 cm., and there 
has been an overall rise in level of 6 cm. over the past 40 years. These 
fluctuations, like the seasonal changes, probably depend on varying 
climatic conditions. The long-term rise is generally attributed to the 
melting of glaciers and polar icecaps, but in some regions subsidence 
or elevation of the land due to modifications in the earth’s crust may 
be as important as changes in the level of the ocean. Although the 
southern part of England seems to be sinking in relation to the sea 
level, there is no change on the east coast of Scotland. Much has been 
written on the subject in the light of historical, archeological, and 
geographical evidence, and of tide records, but quantitative study is 
difficult without larger and more detailed measurements of both land 
and sea levels and without more knowledge of modifications in ice 
cover. Some of the changes—reaching as much as 15 cm. in 100 years 
in certain cases—are sufficiently large to warrant serious consideration 
in the planning and cost of seawalls. 
EFFECT OF OCEANS ON CLIMATE 
The atmosphere is very transparent to the sun’s short-wave radia- 
tion, little of which is absorbed and that mainly by the water vapor and 
carbon dioxide in the air. Nearly half of the incoming radiation is 
reflected by the clouds and the surface of the sea and land; the rest is 
absorbed by the water and land surfaces. Storage by water is more 
efficient, first because water needs five times as much heat as does rock 
to raise its temperature by the same amount, and then because the 
overturning and mixing of water makes it store its heat deep down 
as well as at the surface. In the temperate regions, the effect of sum- 
mer heating can often be detected down to 100 m. by the end of the 
season. Because of the greater specific heat of water and because of 
mixing, the day temperature rises less and the night temperature falls 
less at sea than on land. In the Sahara the night temperature can be 
30° C. less than the day temperature, but in the same latitude over the 
ocean the difference is likely to be less than 2° C. Whence the contrast 
between maritime climate and continental climate. 
Winds and currents play a large part in controlling climate. As far 
as we know, there is a rough balance of incoming and outgoing radia- 
tion over the world as a whole, but there are significant differences 
between one region and another. Winds and currents prevent the hot 
climates from getting hotter and the cold from getting colder by trans- 
porting large amounts of heat, mainly from lower to higher latitudes. 
The atmosphere has an active circulation, probably because it receives 
heat at the bottom from the land and sea, mainly by conduction and 
from water vapor, and is cooled at the top by radiation to space. But 
the oceans are heated and cooled at the same level, since the inward 
