The Colt Army Special was made from 1908 until 1927 when it was renamed as the Colt Official Police.
This is a medium framed revolver, with the same frame that Colt used on all medium frames up until 1969.
This is basically the same design with many parts interchanging with the later Colt Python.
The Police Positive Special was made from 1908 and in one form or another right up into the 1990's.
This was Colt's small frame, and was used on such guns as the Detective Special, Cobra, Agent, Diamondback, and other small framed revolvers.
The two guns are virtual copies or each other, one smaller than the other, but no parts interchange.
As a pure shooter, the Army Special is the stronger gun.