Christian Huygens and William Derham and 18th Century Precursors to the Habitable Zone

Both Christian Huygens and William Derham expressed ideas that are prescient to the concept of a circumstellar habitable zone: liquid water is a precondition for life, there is a region within the solar system within which liquid surface water can exist upon planets, the stars are suns around which planetary systems should be common, these extrasolar planetary systems may include habitable worlds. Although neither author explicitly developed the phraseology of an exoplanetary habitable zone based upon liquid water, such a concept would follow from their writings.