Something that's been puzzling me for a short while and I haven't seen
discussed befo How does the wet bulb operate when the dry bulb temp
is below freezing? Googling brings up some information, which
suggests that ice is allowed to build-up around the bulb but I haven't
gleaned much more from that source.

As the the lower wet bulb temperature results from evaporation from the
muslin surrounding the bulb, wouldn't that cease (in favour of some
sublimation, admittedly) when the water freezes. And wouldn't the
water freezing, which releases heat as it does so, affect the reading
around freezing point?

- Tom.