Moseley didn't develop a Periodic Table.
Mendeleev's Periodic Table placed the elements in order of increasing atomic mass, but there were some anomalies.
Iodine (126.9 u) had a lower atomic mass than tellurium (127.6 u), and nickel (58.6 u) had a lower atomic mass than cobalt (58.9 u).
Moseley showed that these anomalies vanished if the atoms were arranged in order of increasing atomic number. Thus, 52-Te comes before 53-I, and 27-Co comes before 28-Ni.
Periodic Tables ever since then have listed the elements in order of atomic number.
