Dear Roger,  Greetings from The Bronx!  In your quest to better
understand the operation of the "Swanee Whistle" please refer to page
592 in the "Encyclopedia of Automatic Musical Instruments" by Bowers.
On it are three photographs: the first photo shows just the Swanee
Whistle, the second photo is of the device mounted in front of other
components, whilst the third photo shows part of the operating
mechanism.  Below the photos is an explanation of how the mechanism
works.

Here are three videos containing the Popper's Roland in operation:

1. video #1 is from an upcoming auction (maybe you'd like to bid
on it?), it shows the Swanee Whistle in action:
http://www.youtube.com/watch?v=GP4rWE1F_NQ
 

2. video #2 also shows a playing Roland, but not much action from
the Swanee Whistle:
http://www.youtube.com/watch?v=E5Ze0v1ZRFI
 

3. video #3 shows 3 different mechanical music machines, including
a Roland (the second instrument to play):
http://www.youtube.com/watch?v=IbLYf3rZcy0
 

Hope this helps,

Sincerely,
Dale F. Rowe
Bronx, New York