Accessing a Javascript variable in embedded Ruby

Hi, I have a form that I am observing with observe_field

<%= observe_field :guess,   :frequency => 0.6,   :update => 'ajaxWrapper',   :url => {:action => 'feedback', :only_path => false},   :with => 'correct=#{@chapter[0])}' %>

When I construct the parameters for the URL, I'd like to use a javascript variable to index into the chapter array. (Instead of always selecting the first element as in the example above)

Is that possible? I can't figure out how to access the variable from within the #{}