Nov 272015


Today is the birthday (1701) of Anders Celsius, a Swedish astronomer, physicist and mathematician. He was professor of astronomy at Uppsala University from 1730 to 1744, but traveled from 1732 to 1735 visiting notable observatories in Germany, Italy and France. He founded the Uppsala Astronomical Observatory in 1741, and in 1742 proposed a temperature scale which now bears his name.

Celsius was born in Uppsala in Sweden, but his family originated from Ovanåker in the province of Hälsingland. Their family estate was at Doma, also known as Höjen or Högen (locally as Högen 2). The name Celsius is a latinization of the estate’s name (Latin celsus “mound”).

As the son of an astronomy professor, Nils Celsius, and the grandson of the mathematician Magnus Celsius and the astronomer Anders Spole, Celsius chose a career in science. He was a talented mathematician from an early age. Anders Celsius studied at Uppsala University, where his father was a teacher, and in 1730 he too, became a professor of astronomy there.


In 1730, Celsius published the Nova Methodus distantiam solis a terra determinandi (New Method for Determining the Distance from the Earth to the Sun). His research also involved the study of auroral phenomena, which he conducted with his assistant Olof Hiorter, and he was the first to suggest a connection between the aurora borealis and changes in the magnetic field of the Earth. He observed the variations of a compass needle and found that larger deflections correlated with stronger auroral activity. At Nuremberg in 1733, he published a collection of 316 observations of the aurora borealis made by himself and others over the period 1716–1732.

Celsius traveled frequently in the early 1730s, including to Germany, Italy and France, when he visited most of the major European observatories. In Paris he advocated the measurement of an arc of the meridian in Lapland. In 1736, he participated in the expedition organized for that purpose by the French Academy of Sciences, led by the French mathematician Pierre Louis Maupertuis (1698–1759) to measure a degree of latitude. The aim of the expedition was to measure the length of a degree along a meridian, close to the pole, and compare the result with a similar expedition to Peru, near the equator. The expeditions confirmed Isaac Newton’s belief that the shape of the earth is an ellipsoid flattened at the poles.

In 1738, he published the De observationibus pro figura telluris determinanda (Observations on Determining the Shape of the Earth). Celsius’ participation in the Lapland expedition won him much respect in Sweden with the government and his peers, and played a key role in generating interest from the Swedish authorities in donating the resources required to construct a new modern observatory in Uppsala. He was successful in the request, and Celsius founded the Uppsala Astronomical Observatory in 1741. The observatory was equipped with instruments purchased during his long voyage abroad, comprising the most modern instrumental technology of the period.

In astronomy, Celsius began a series of observations using colored glass plates to record the magnitude (a measure of brightness) of certain stars. This was the first attempt to measure the intensity of starlight with a tool other than the human eye. He made observations of eclipses and various astronomical objects and published catalogs of carefully determined magnitudes for some 300 stars using his own photometric system (mean error=0.4 mag).


Celsius was the first to perform and publish careful experiments aiming at the definition of an international temperature scale on scientific grounds. In his Swedish paper “Observations of two persistent degrees on a thermometer” he reports on experiments to check that the freezing point is independent of latitude (and of atmospheric pressure). He determined the dependence of the boiling of water on atmospheric pressure which was accurate even by modern day standards. He further gave a rule for the determination of the boiling point if the barometric pressure deviates from a certain standard pressure. He proposed the Celsius temperature scale in a paper to the Royal Society of Sciences in Uppsala, the oldest Swedish scientific society, founded in 1710. His thermometer was calibrated with a value of 100° for the freezing point of water and 0° for the boiling point. In 1745, a year after Celsius’ death, the scale was reversed by Carl Linnaeus to facilitate more practical measurement. Celsius originally called his scale “centigrade” derived from the Latin for “hundred steps”. For years it was simply referred to as the Swedish thermometer.


Celsius conducted many geographical measurements for the Swedish General map, and was one of earliest to note that much of Scandinavia is slowly rising above sea level, a continuous process which has been occurring since the melting of the ice from the latest ice age. However, he wrongly posited the notion that the water was evaporating.


In 1725 he became secretary of the Royal Society of Sciences in Uppsala, and served at this post until his death from tuberculosis in 1744.

Here’s a map of the world showing all the nations that use the Celsius scale, and those that use the Fahrenheit scale. Hmmmm.


Barely visible are the Bahamas, Belize, the Cayman Islands, and the Republic of Palau.

This is why I often use both Celsius and Fahrenheit in my recipes (sop to the USA). Anyway, I’m slightly haphazard about metric versus imperial measure in general because I’m not a big fan of precision in cooking in general (except baking). It’s hard enough for me to include measures at all. With oven temperatures I give exact measures because ovens come that way, but I don’t think in those terms. I think in heuristic terms, such as hot, medium, etc. Partly this is because ovens are so variable. At one time I used an internal oven thermometer, but these days I wing it. My oven in China never got hot enough for me, and my current one seems to have two settings – furnace and off. I manage.

The cloudberry (Rubus chamaemorus) is native to Sweden and very popular there. Sadly, it is very difficult to cultivate, so it’s almost impossible to find fresh cloudberries outside of northern latitudes. Nonetheless, I am going to give you a recipe for cloudberry ice cream made with fresh berries. Slightly modified, this recipe can be made with cloudberry preserves, which are much more easily found worldwide. I am choosing ice cream for today’s celebration because Celsius determined that the freezing point of pure water was invariant (and so became one end of his temperature scale). Also, Swedes are the heaviest consumers of ice cream in the world. Cloudberry ice cream and chilled cloudberry cream are common favorites.


Hjortronglass (Cloudberry Ice Cream)


18 ounces fresh cloudberries (about 4 cups)
¾ cup sugar, divided
4 large egg yolks
kosher salt
1½ cups heavy cream, divided
2 tsp fresh lemon juice


Cook the berries and ¼ cup of sugar in a medium saucepan over medium heat until the berries are soft and starting to release their juices. Increase the heat to medium-high and bring to a boil. Boil, stirring occasionally to prevent sticking, until the mixture thickens slightly, about 5 minutes. Set aside ½ cup of sauce. Purée the remaining sauce in a blender until smooth, and strain through a fine-mesh sieve into a measuring glass (you should have about 1 cup). Let cool.

Whisk the egg yolks, a pinch of salt, and the remaining ½ cup sugar in a medium bowl until lightened in color. Bring 1 cup of cream to a boil in a medium saucepan. Immediately remove from the heat and very gradually whisk half of the cream into the egg yolk mixture. Be very careful here because you can easily scramble the egg. Whisking constantly, add the egg mixture to the remaining cream in the pan and then cook over medium heat, stirring constantly, until the custard is thickened, about 2 minutes. Strain through a fine-mesh sieve into a large bowl. Chill until cold.

Whisk the custard, berry purée, lemon juice, and remaining ½ cup of cream until smooth. Process in an ice cream maker of your choice.

Spoon in the reserved berry sauce, then scrape the ice cream into an airtight container (you want nice streaks of sauce still visible). Cover and freeze until firm, at least 2 hours.