In June and July in Paris Betancourt writes out a Memoir about the plunger piston lock –that he had invented in 1801- to be presented at the Académie des Sciences. The Mémoire sur un nouveau systéme de navigation intérieure, after being examined by a committee of the Académie, is published in 1808.

It is possible that Betancourt invented the metallic thermometer at this time, the authorship, however, is attributed to Breguet and it will be him who will make them in mass and commercialize them.

It seems that Betancourt had already thought of staying in Paris due to the political circumstances in Spain: the discredit of Godoy, who accumulates power, the conspiracies of Fernando VII, the discouragement after the defeat at Trafalgar, the arrogance of Napoleon, who in September orders his troops to enter the Peninsula, in theory to pass to Portugal…