Sentence:  ... when the wind was that way, which was often, the house was full of the stench of this sulphurous combustion of the earth's excrement. But even on <WSD>windless</WSD> days the air always smelt of something under-earth: sulphur, iron, coal, or acid. 
Meaning of the word marked with <WSD> tags:  Devoid of wind; calm.