trouble with FixedHeader

trouble with FixedHeader

I'm trying to use FixedHeader for my website.
I downloaded FixedHeader.js and put it in vendor/assets/javascripts. I
have //= require FixedHeader in application.js.
In colleges.html.erb I've set a class of table-fixed-header to each of my
two tables. In colleges.js, I've got var oTable =
$('.fixed-table-header').dataTable(); new FixedHeader( oTable );.
In the development environment, when I go to inspect element > resources
(in chrome), FixedHeader.js loads, but there's 1 problem with colleges.js:
it says...
var oTable = $('.fixed-table-header').dataTable();
Uncaught TypeError: Object [object Object] has no method 'dataTable'
new FixedHeader( oTable );
What can I do to get this to work?