A partition of unity is a mathematical concept in geometry. I want to know when and in what context this concept appeared.
Partitions of unity were formally introduced by Dieudonne (C. R. 205 (1937) 593-595), and for some time they were even called "Dieudonne decompositions". However is some special cases they were used by Whitney (TAMS, 36 (1934) 63-89). This information is taken from Hormander, Analysis of Partial differential operators, vol. I, comments to Chapter I.