Well, Mason's message surprised me :
First, was obsolescence a very popular term among economists around 
1900? It does not appear in Marshall's Principles index.
Second, obsolescence is only a small part of what Schumpeter intended to 
describe with "creative destruction" as far as I understand it (an 
explosive, exponential and cumulative process with far fetched effects 
ignated by some initially localized innovation).

Alain Alcouffe