page_title: Johann Hasler
section_title: Medicine and science
hierarchical_section_title: Johann Hasler / Medicine and science
caption_attribution_description: English: An image of a double bulb (dutch) thermometer, with temperature shown on a 1-9 scale similar to that presented by Johann Hasler in 1578
context_page_description: Johann Hasler, also known as Haslerus, was a 16th-century Swiss theologian and physician. He is known for his association with a group of antitrinitarians including Johann Sylvan and Adam Neuser and for developing Galen's concept of heat and cold into the idea of a scale of temperature
context_section_description: Galen's theory of medicine used the idea of the four humours (earth air fire and water) characterised by four qualities (moist, dry, warm, cold), linked as - Earth: dry cold; Air: moist, warm; Fire: dry, warm; Water: moist, cold. Hasler followed Galen in considering temperament (cf temperature) as an important characteristic of both persons and medicines. Galen had experimented with mixing boiling water and ice to establish a "neutral" temperature, and posited four degrees of cold and four degrees of warmth on either side of this neutral zero point. This formulation still envisaged warm and cold as distinct, opposed entities. Hasler saw that the nine points of Galen's model could be united into a single scale from 1 (coldest) to 9 (hottest). 
   A thermometer with a 1-9 scale was described in 1624.
  He also aligned his 1-9 temperature scale with latitude, with one end of the scale corresponding to the hot equator, the other end to the cold arctic, as shown in the reproduction on the right. The diagram shows that a similar scaling applies to humidity. It appears that Hasler envisaged the underlying scales as continuous - this is implied both by the mapping to latitude, and by the presentation of more detailed, sub-divided versions of the scales.
  Hasler's works also included comprehensive catalogues of medical substances categorised according to their properties of temperature and humidity, and astrological calendars.
caption: A double bulb (Dutch) thermometer with 1-9 temperature scale. From Leurechon's Recreation mathematique
exif: {}