# Definition:Celsius

## Definition

Its two reference points are:

$0 \cels$, which is set at the melting point of water.
$100 \cels$, which is set at the boiling point of water, as defined at sea level and standard atmospheric pressure.

A temperature measured in Celsius is often referred to as so many degrees Celsius.

### Conversion Factors

 $\ds$  $\ds 1$ degree Celsius $\ds$ $=$ $\ds 1 \cdotp 8$ degrees Fahrenheit

### Symbol

The symbol for the degree Celsius is $\cels$.

## Also known as

The Celsius scale is also known as the centigrade scale, but this usage has been obsolete since $1948$.

## Source of Name

This entry was named for Anders Celsius.

## Historical Note

The Celsius scale is based on that proposed in $1742$ by the astronomer Anders Celsius.

He defined the upper and lower reference points from the melting and boiling points of water.

These were initially the other way round from their current definitions: $0 \cels$ was for the boiling point and $100 \cels$ was for the melting point.

Celsius originally called it the centigrade scale, but for various reasons the name was a source of confusion, and so in $1948$ the name Celsius was adopted.

This is the system of measurement of temperature that is generally taught in schools.