Sentence:  To avoid which, we will take any pains ...; we will dive to the bottom of the sea, to the bowels of the earth, five, six, seven, eight, nine hundred fathom deep, through all five <WSD>zones</WSD>, and both extremes of heat and cold […]. 
Meaning of the word marked with <WSD> tags:  Each of the five regions of the earth's surface into which it was divided by climatic differences, namely the torrid zone (between the tropics), two temperate zones (between the tropics and the polar circles), and two frigid zones (within the polar circles).