A very rare and important chart of the discoveries along the coasts of North America and Asia shortly after James Cook’s famous Third Voyage.  This chart, which was made by Lt. Henry Roberts, is commonly referred to as the “Legendary Lost Chart of Captain James Cook” for its depiction of the Pacific Northwest discoveries that were not included in the official published account following Cook’s untimely death in 1779. 
Roberts, who had attained the rank of Masters Mate and sailed along with James Cook on the HMS Resolution, had originally been commissioned to draw the chart describing the official version of Cook’s ill fated third voyage and was slated to be published in the Atlas that was to accompany A Voyage to the Pacific Ocean…, London, 1784.  However, it is claimed that “because of disputes among the editors, it was not included in the final publication of the official account.”
As it was, the Roberts’ plate was sold to William Faden who went on to publish the chart separately in the same year as a Chart of the NW Coast of America and NE Coast of Asia explored in the Years 1778 & 1779, the official version that was included in the above mentioned Atlas.  The differences between the two version are important.
Roberts’ depiction includes the Arctic discoveries of Samuel Hearne, a full decade before his journal and maps were to be published.  Hearne, a fur trader for the Hudson’s Bay Company, is known as the first European to reach the Arctic Ocean by an overland route via the Coppermine River in Northern Canada.  As such, Roberts’ chart is the first to publish, what had until then been only drawn in manuscript form by  Hearne, of the impossibility of a Northwest passage through Hudson’s Bay.  Furthermore, Roberts’ chart depicts in much greater detail the interior of the North where traders for the Hudson’s Bay Company  plied their trade.
The question as to why Roberts’ chart may have been dismissed from the official account could be a result of the involvement of Alexander Dalrymple in the selection process.  On one hand, Dalrymple may have harboured ill feelings towards Cook for having been chosen, instead of him, to lead the Second Pacific Voyage in 1772-75 that ultimately disproved the myth propounded by the likes of Dalrymple himself, of Terra Australis Icognita.  As such, Dalrymple may have wanted to downplay Cook’s achievements and discoveries.  Secondly, it could be argued that the Hudson’s Bay Company may have willfully tried to suppress information relating to the Northern interior to protect their commercial interests.
It is thus quite fitting that when Roberts’ chart is compared to the official published version of James Cook’s Third voyage, it is his chart that is historically more precise, aesthetically pleasing and coveted by collectors for its rarity.
(Sources:Wagner, Northwest Coast #700, BLR#30001, Cohen&Taliaferro Catalogue#62, Campbell A Cook Mystery Solved , Sep.85 )