After Cook died he helped lead the ships on the remainder of their course , also completing Cook 's account of the voyage .
He served under James Cook on his last voyage around the world , specialising in taking important astronomical readings using a sextant .
After James Cook died James Cook helped lead the ships on the remainder of their course , also completing James Cook 's account of the voyage .
He served under James Cook on his last voyage around the world , specialising in taking important astronomical readings using a sextant .