Page 255 - NS-2 Textbook

250 NAUTICAL SCIENCES

A sample weather map showing frontal systems outlined by lines called isobars, drawn through points of equal pressure. Isobars never join or
cross. Some may run off the chart, and others will form irregular ovals that define areas of high and low pressure. When the lines are dose
together they represent areas of higher wind intensity, with the direction of the wind from high- to low-pressure areas.

acts like the glass on a greenhouse. It lets the short solar to the Celsius (C) scale, in which the freezing point of
rays pass through; the Earth absorbs these and then rera- water is 0 degrees and its boiling point is 100 degrees.
diates the heat as long heat waves. But these long heat The Celsius scale is in the metric system, which one
waves cannot all get through the atmosphere because day is supposed to be the principal measurement system
they are absorbed by the water vapor. So they stay within used in the United States, as it is already in most of the
the If greenhouse" in a continual cycle. You ,vill notice rest of the world. It is likely, howevel; that for a good
this especially on hot, overcast sununer nights when the many years conversion of temperatures from one scale to
humidity is high. the other will be a conunon necessity.
The atmosphere thus acts almost like an automatic There are 5 degrees of Celsius temperature for every
thermostat in controlling the Earth's heat. It screens out 9 degrees of Fahrenheit. Since 32 degrees F is equivalent
the dangerous solar radiation and reflects some of the ex- to 0 degrees C, to change a Fahrenheit reading to Celsius
cess, and it acts as an insulator to keep most of the heat you subtract 32 degrees and then multiply the remainder
from escaping at night. Without the atmosphere, the by 5/9 (formula: C = 5/9[F - 32]). Let's say you want to
Earth would be like the Moon-with boiling tempera- change 59 degrees F to Celsius. Subh'acting 32 degrees
tures during the day and subfreezing temperatures dur- from 59 degrees leaves 27 degrees. Multiply 27 degrees
ing the night. by 5/9 and you get 15 degrees C.
To change a Celsius reading to Fahrenheit, the
process is reversed. Sinlply multiply the Celsius temper-
MEASURING TEMPERATURE
ature by 9/5, and add 32 degrees (formula: F = 9/5 C +
A thermometer is an instrument for measuring tempera- 32 degrees). Using the figures from the previous exam-
ture. It is a narrow glass tube filled with alcohol or mer- ple, to change 15 degrees C back to Fahrenheit, first mul-
cury. The liquid rises and falls within the bore as the rise tiply it by 9/5, which gives you 27 degrees; then add 32
and fall of the temperature causes the liquid to expand degrees. You are now back to the original 59 degrees F.
and contract. A temperature scale is marked on the hibe. Most inexpensive house thermometers are filled
The Navy and most civilians in America usually use with red-dyed alcohol. If you compare a mercurial ther-
thermometers with a Fahrenheit (F) scale. On that scale, the mometer with a red-alcohol one you will note that the
freezing point of water is 32 degrees and the boiling point top of the cohunn of liquid is in the shape of a curve,
is 212 degrees. Temperatures in meteorology and most called a meniscus. Because of the different characteristics
other sciences, however, moe usually expressed according of the liquids involved, the accurate reading for an alco-