Starting in November, 1768, the Isis put in successively at Cadiz, the Canary Islands, Goree, the Cape Verde Islands, Martinique, St. Domingo, Terra Nuova, the Canaries, Cadiz again, and reached Aix Island on the 31st of October, 1769.
The watches, carried through climates alternately cold, hot, and temperate, had experienced every vicissitude of climate, and at the same time had been exposed to all the variations of the sea, in the roughest season of the year.
After this trial, which had redounded so much to his honour, Berthould obtained the rank and pension of an inspector of nautical watches.
This expedition had other results which concern us more particularly. Fleurien took a number of astronomical observations, and hydrographical surveys, which resulted in a well-founded condemnation of the maps of his country.
"For a long time," he says, in his account of his voyage, "I did not attempt criticism of the maps belonging to the Society; I wished to limit myself to giving new details by which they might be rectified; but I found such numberless and dangerous mistakes, that I should have considered myself culpable towards mariners if I had neglected fully to point them out."
A little further on he justly criticizes the maps of a geographer who had at one time been famous.
"I will not undertake," he says, "to enumerate all the errors which I have found in M. Bellin's maps. Their number is infinite. I shall content myself simply with proving the necessity for the work I did, by indicating the more glaring faults, either by comparing the positions of various places upon his maps, with the positions they should have occupied if M. Bellin had been willing to use the astronomical observations which have been published at various times; or by comparing other positions with those which we have determined by our own observations."
Lastly, after giving a long list of errors in the situation of the most frequented places of Europe, of Africa and America, he winds up with these judicious words:—
"Upon glancing at a list of the various errors I have discovered in M. Bellin's maps, one is led to a reflection, sad but true and inevitable—if the maps of the best known part of the globe, and on which the greater number of observations have been taken, are so far from correct, what exactitude can we hope to find in maps representing less frequented shores and islands, drawn and arranged by guess-work?"
Up to this time the watches had been examined separately and by different judges. Now arose the question of submitting them simultaneously to the same test, and of seeing which would come out victorious.