construction maison moderne lyon

>> derek: how did celsius define his scale? >> michael: uh... he took the temperature water freezes at and said that's zero and then he took the temperature it boils at and says that's ahundred. and he figured a hundred was a good amount of demarcations to make in between the two. right? >> derek: yeah. except that's not what he did.>> michael: really? >> derek: celsius never devised nor used the scale that now bears his name. >> michael: are you kidding me? >> derek: no, michael, i'm not! this is the swedish town of uppsala,located 70 kilometers north of stockholm. so this is the house where celsius lived.in 1741 he was professor of astronomy at

uppsala university. and this is thefirst ever celsius thermometer... or is it? >> this is the first scale of anders celsiusadded onto... or, added onto an old thermometer. so we have delisle' scale on the lefthand side and celsius' new scale in the right. >> derek: these few markings show that celsius came up with the idea of separating the freezing andboiling points of water by 100 degrees. he made his first observations with thescale on christmas day 1741. but have you noticed something strange about this scale? i mean, 50 is marked in the middle butthe numbers increase down towards the

bulb of the thermometer. so, celsius hadhis scale upside down. he set zero degrees at the boilingpoint of water and a hundred at the freezing point. why would he do this? well, for one thing celsius was just following theconvention of the other scale on the thermometer. delisle' scale also hadzero degrees for the boiling point of water increasing down to 150 for hisfreezing point. and a likely reason both of them used upside down scales isbecause they avoid negative numbers. in sweden it gets much colder than freezingbut never warmer than boiling water so

you don't have to worry about peskyminus signs and this helps avoid logbook errors. i think it would be really weird if youhad water boiling zero degrees and freezing at a hundred.wouldn't that be strange? although it might seem strange today,there is no objectively good reason for preferring an ascending scale over adescending one for measuring degrees of something, like hot or cold. in fact, when celsius died oftuberculosis in 1744, he was still using this inverted scale.

so who reversed it? who do we have tothank for the modern celsius temperature scale? well in 1745, just a year after celsius'death a new column appears in the uppsalatemperature record using the modern scale and at the top it's got theheading "ekstrã¶m" now ekstrã¶m was the instrument maker at uppsala. in 1747another column is added with the heading strã¶mer who was celsius' successoras professor of astronomy. again, it's got the same modern scale. but it's another professor at uppsala who claims that he reversed the scale: that's the famous biologist carllinnaeus. he says he reversed the scale

when he ordered a thermometer fromekstrã¶m for his greenhouse. whoever it was, we know that by 1745there was an operational thermometer at uppsala university with a scale that wenow all know as the celsius temperature scale. except... this was not the first suchthermometer ever created. in 1743 the year before celsius died, a frenchscientist working independently in lyon created a thermometer with zero degreesat the freezing point of water and a hundred at the boiling point. his name was jeane pierre christin. so why isn't it called a degree christin instead of a degrees celsius?

well, for a long time this temperaturescale wasn't referred to using either of their names and instead it was justcalled the "centigrade scale," meaning a hundred steps. the problem with this was "centigrade"has other meanings in french, spanish and italian, where a grade specificallyrefers to one one-hundredth of a right angle. so to eliminate this confusion theinternational bureau of weights and measures in 1948 decided to rename thecentigrade scale after a scientist bringing it into alignment with othertemperature scales like kelvin and fahrenheit. they chose celsiuspossibly due to a popular 1800's german

chemistry textbook by a guy named berzelius. in it, berzelius identified celsius as the first to devise atemperature scale with zero at water's freezing point and a hundred at itsboiling point propagating the myth that celsius created this scale. so is celsiusundeserving of having his name immortalized on weather maps around the world? well, no. i mean making two marks anddeciding on a number of degrees in between them that is the easy part whichothers could, and as history shows, did do... but what celsius did was he establishedwhich physical processes could reliably produce a fixed temperature. at the timewhen he was working, there were some 30

different temperature scales in use. somethermometers had 18 different scales on them, some more reliable than others. forfixed reference points one scale used the deepest cellar of the paris observatory, others used the melting temperature ofbutter, the internal temperatures of certain animals, or the hottest day insummer in italy, syria or senegal. these dubious scales combined, withinconsistent thermometer construction made recording accurate temperaturesnearly impossible, not to mention sharing those temperatures with other scientistselsewhere. celsius solved this problem in a number of ways: he demonstrated thatmelting snow maintains a fixed temperature

regardless of latitude or ambientpressure. he also determined the precise relationship between boiling point ofwater and the ambient pressure, so that thermometers could be calibrated underany conditions. he made it possible to establish auniversal reliable system of temperature measurement and this is why celsius' name is a unit of temperature, even though the scale itself was not createdby him and in fact today the celsius scale is no longer defined by either ofwater's phase transition points, instead it is based off the kelvin scale andthat scale is defined by setting the triple point of water,

where solid, liquid, and gas all exist inequilibrium at exactly 273.16 kelvin. this fixes the size of a degree kelvin,which is exactly the same as the size of a degree celsius. the zero point of thecelsius scale is set a 273.15 kelvin. and what all this meansis that today pure water boils at 99.974 degrees celsius and freezes at negative 0.0001 celsius. this precision in anearly universal system of temperature measurement is thanks to a huge numberof scientists so the c after the degree symbolstands not only for celsius or christin or carl linnaeus, but for the communityof scientists whose work over centuries

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