148

NICHOLLS'S SEAMANSHIP AND NAUTICAL KNOWLEDGE

The space between these two points is divided into equal parts cal
degrees; the following systems of graduating have been adopted.

Fahrenheit
Centigrade
Absolute.
Re'aumtn

Boiling point - -Freezing point - -
212° 32°
100° 0°
373°A 273°A
80° 0°

The spacing of the degrees in the Absolute
scale is the same as in the Centigrade, but there
are no minus readings with the former.

The real reason why Fahrenheit fixed the
zero of his scale as 32 degrees below the freez-
ing point of water seems to be lost in the mists
of obscurity, but the zero of the Absolute scale
is based on the doctrine that gases contract on
being cooled, their volume being diminished
with loss of temperature. The zero represents
the temperature at which a gas would have no
volume, it would then cease to exert pressure,
or be capable of developing energy.

The figure represents a portion of a ther-
mometer showing the Absolute scale to the left
side of the thread of mercury and the Fahrenheit
scale to the right. The space between freezing
point and boiling point is divided into 100 parts,
0 to 100, in the Centigrade scale; and 180 parts,
32 to 212, in the Fahrenheit scale, so that
100° C. is equal to 180° F. It is sometimes
required to convert one reading into the other
which may be done as follows by assuming that
Fahrenheit called the freezing temperature of
water 0 as he might have done.

Example.—Convert 310° Abs. into the cor-
responding Fahr. reading.

310 Absolute—273=37 Centigrade
Fahr. reading Cent, reading
?ahr. range ~~ Cent, raifge

JL = 2L — 37 x 180 _ 333

180 "~ 100 *" * ~~ 100 ~~ If
«= 66-6 + 32 = 98-6 An*.

510-

300-

FP.

270—

260 —

-1C

Fig 15—Fahrenheit a
Absolute Scales.