Using Highcharts in Rails

Using Highcharts in Rails

I'm learning Rails and just wanted to use Highcharts in my app.
These are my steps:
I added highcharts-rails in my Gemfile,
ran 'bundle install',
added '//= require highcharts' in my application.js
and finally changed the javascript_include_tag in application.html.erb to
'<%= javascript_include_tag "application", "highcharts" %>'
Now I'm getting this error:
Sprockets::FileNotFound in PowerReadings#index Showing
/Users/ggn/Sites/Rails/homecontrol/app/views/layouts/application.html.erb
where line #50 raised:
couldn't find file 'highcharts' (in
/Users/ggn/Sites/Rails/homecontrol/app/assets/javascripts/application.js:17)
I don't know what's wrong here. Any hints?