In article ,
John Hall writes:
I think the attraction of wet bulb temperature is that it can be
measured directly, by having a thermometer whose bulb is encased in wet
muslin, or some similar device, rather than needing to be calculated.
Once you've measured dry and wet bulb temperatures, then you can use
them to calculate the relative humidity and the dewpoint. Your modern
weather station may be able to measure the humidity directly, but I
don't think that "traditional" simple met instruments could do this, so
observers would derive the humidity from the wet bulb reading rather
than vice versa.

One other reason for measuring (or calculating) the wet bulb temperature
that I forget to mention. When temperatures are close to freezing, the
wet-bulb temperature becomes of interest in its own right, since whether
or not it is below zero determines whether ice or snow will melt.
--
John Hall
Johnson: "Well, we had a good talk."
Boswell: "Yes, Sir, you tossed and gored several persons."
Dr Samuel Johnson (1709-84); James Boswell (1740-95)