In 1940 Siple and Charles F. Passel conducted experiments on the time needed to freeze 250 grams of water in a plastic cylinder that was exposed to the elements.
Wind chill accounts for loss of heat when warm air around a body is replaced with colder air.
The factor is an indication of the effect of the combination of air temperature and wind speed on human comfort and safety. 33.0 Forecasts made with these equations are reasonably sufficient, though work is being done at this very moment to obtain a better index or factor.