Ole C. Roemer (1644-1710).
Danish astronomer. Ole C. Roemer is in 1702 the first to define a thermometric scale, in which the point of boiling water and "the point of snow" - that is 0 degree Celsius - are fixed points. Those two fixed point were (unfortunately) classified as 60 degree and 7.5 degree (later 8 degree).
Where as Ole Roemer used alcohol as thermal expansion; Farhrenheit used mercury. The thermometric scale, introduced by Fahrenheit in the early years of the 18th century, had as zero the temperature of freezing material, matching minus 18 degree Celsius. As its other fixed point Fahrenheit used the standard temperature of the human body, defined as 96 degree.
In 1742 Celsius (q.v.) for the first time used a scale, divided into 100 graduations within those two fixed points earlier suggested by Ole Roemer.
Picture: Part of a Temperature-register based on a particularly cold winter in Copenhagen 1708/09. In the register Ole Roemer defines "8" as 0 degree, and "0" as minus 15 degree Celsius. The two parts are to be read in continuation. Vertical each day - from December 26th 1708 to April 6th 1709 - is registered. Horizontal the temperature is noted.
Lit: "Termodynamik", by Erik Both and Gunnar Christiansen, DTU, Denmark, 1995. And "Ole Roemer", by Axel V. Nielsen, Ole Roemer-Observatorium, Aarhus 1944.
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