probably made in London
This thermometer was made around 1900, probably by L. Casella, a scientific instrument maker based in London. This form of thermometer was invented by James Six (1731-93) of Canterbury in 1780.
The instrument records maximum and minimum temperatures without the observer having to be present. The alcohol pushes a column of mercury, which in turn moves one steel index into the maximum temperature position, the other to the minimum.
This pattern of thermometer uses the scale of Daniel Gabriel Fahrenheit. His 1724 scale had three fixed points: 0 - freezing point of a mixture of ammonium chloride and snow; 32 - freezing point of water; 96 - and mouth temperature of a healthy person.
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