Javascript error in Timeline plugin

Hi -
I'm trying to get the Timeline plug-in to work. My timeline seems to be getting the items correctly but doesn't display anything (not even the timeline background.)

Here's the page:

There's a Javascript error at this line (line 61 in the source):
saying that $$ is not defined.

It would be great if someone could tell me how to fix this error, or if the people responsible for the Timeline plug-in could fix whatever is causing this. Thanks for your time.

That error is related to the Prototype Javascript library.

You can enable Prototype in Omeka on the General Settings page (the setting is named "Enable Prototype").

That worked! Thank you very much.