Characterizing himself "Surgeon-Accoucheur" on the title page, Dewhurst lectured in 1827-8 on anatomy and physiology, and served as a ship's surgeon, making voyage to Greenland and its surrounding seas in 1824. During that voyage he  studied large Arctic creatures, especially whales. In the decade after his return Dewhurst prepared this description of polar sea life.  Whales were of especial interest in this period, because of the use of their blubber in many household objects, and the value of their oil for lamps, as whale oil burned without soot. Dewhurst's work was one of the first studies to examine the different species of whales, as well as dolphins and other marine life. Digital facsimile from the Internet Archive at this link.