Sentence:  I may cast my readers under two general divisions: the mercurial and the <WSD>saturnine</WSD>. The first are the gay part of my disciples, who require speculations of wit and humour; the others are those of a more solemn and sober turn, who find no pleasure but in papers of morality and sound sense. 
Meaning of the word marked with <WSD> tags:  Of a person: having a tendency to be cold, bitter, gloomy, sarcastic, and slow to change and react.