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460 THERMOMETERS
Thermometers.
The well known instrument called thermometer is used to
measure the common temperatures, as from 40 degrees below
zero to 450 degrees above zero, Fahrenheit.
There are in common use three different kinds of ther-
mometer scales, namely the Fahrenheit, the Celsius (also called
the centigrade), and the Reaumur. The Fahrenheit is used in
England and in the United States. The Celsius and the Reaumur
are used in Europe, outside of England. The Celsius is used
the most and is almost universally used in technical books and
all kinds of scientific calculations.
The ratio between those thermometers are:
Thermometers. Boiling point. Freezing point,
Fahrenheit 212 32
Reaumur 8o° o°
Celsius ioo° o°
Following formulas, transpose from one thermometer scale
to another;
4X(,F — 32) 4XC
*- 9
R= ~v~
- _ 5 X(F — 32) _ 5 X R
C- 9
G- 5
Example.
If the temperature is—20 (20 degrees below zero) Fahren-
heit. How much is this in Centigrades ?
Solution
:
5 X (— 20 — 32) 5 X— 52 OR
C = = = — 28f degrees, or
28f degrees below zero on the Celsius thermometer.
Example.
The temperature of a furnace is measured by a pyrometer*
and found to be 1560 degrees Fahrenheit. How much is this in
Celsius degrees?
Solution
:
c = 5 x (1560 -32) = §2<j52i _ 848| degrees Centigrade.
* Pyrometers are instruments used to measure higher temperatures
than what can be measured by thermometers.
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