# What is the second thermometer in the image from the Esperanza Antarctic temperature record?

Today, the Argentinian meteorological service tweeted about a new temperature record for Antarctica of 18.3°C, made on the Espezanza peninsula. This was subsequently reported by many other sources.

The tweet contained an image of a literal analogue thermometer which did show the 18.3°C... but curiously enough, also another thermometer showing merely 10.0°C.

What's that about? Is that 10°C another means of measuring temperature, e.g. some kind of running average temperature? Or is one of the readings simply faulty?

Doing a quick calculation that looks to be around the wet-bulb temperature at the time of observation so that thermometer on the right side should be a hygrometer. Hygrometers measure the level of moisture in the air as opposed to a thermometer that measures the temperature level.

Edit: The calculation was based on a recorded observation scoured from here as finding the history of observations at the station was proving difficult. The observation marked a temperature around 64 degrees F with a relative humidity value of 34%. Using this online based calculator which gives a rough estimate of the Wet Bulb Temperature, the calculated value came out to be 49.47 (F) or 9.7 (C) which was close enough for me to determine that the thermometer on the right was a hygrometer. Aiding that assumption was the fact that thermometers and hygrometers are sometimes paired together for observations.

• Ah, that makes sense. But the answer could use a bit more detail. Commented Feb 7, 2020 at 22:32
• It would be great if you included a link or an example of the calculation, the OP and other readers will find it more instructive. I have a we/dry setup at home and I always have to read the table on the back of the box to get humidity. If there's an equation or something it would be great to know. Thanks!
– uhoh
Commented Feb 7, 2020 at 23:30
• @uhoh: If it is a wet bulb thermometer the relative humidity would be 32% & the dew point would be approx. 1.5 C - according to the spreadsheet I wrote years ago. The relative humidity is vapor pressure divided by saturated vapor pressure @ dry bulb. To get vapor pressure, another 5 or so calculations need to be done: moisture content, moist cont @ wet bulb, enthalpy of vapor press @ wet bulb, enthalpy of liquid water @ wet bulb, enthalpy of vapor press @ dry bulb. Nothing difficult, just time consuming.
– Fred
Commented Feb 8, 2020 at 0:27
• @Fred got it, thanks! I'll look around, and if I don't find an existing Q&A then maybe I'll ask a new question.
– uhoh
Commented Feb 8, 2020 at 0:31
• @Fred I've just asked: How is relative humidity determined from a wet and dry bulb readings?
– uhoh
Commented Feb 8, 2020 at 1:08