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