The Newton scale is a temperature scale devised by Isaac Newton around 1700. Applying his mind to the problem of heat, he elaborated a first qualitative temperature scale, comprising about twenty reference points ranging from "cold air in winter" to "glowing coals in the kitchen fire". This approach was rather crude and problematical, so Newton quickly became dissatisfied with it. He knew that most substances expand when heated, so he took a container of linseed oil and measured its change of volume against his reference points. He found that a litre of linseed oil at the temperature of melting snow grew to 1.0725 L at the temperature of boiling water.

After a while, he defined the "zeroth degree of heat" as melting snow and "33 degrees of heat" as boiling water. He called his instrument a "thermometer".

Thus the unit of this scale, the Newton degree, equals 100/33^rd of a kelvin (or of a degree Celsius) and has the same zero as the Celsius scale.

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• Photo of an antique thermometer backing board c. 1758—marked in four scales; the first is Newton's.