Error with ruby 1.9.1

[sineau]

Using Ruby 1.9.1, i get this error calling to_orgmode.rb:

/usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file -- chronic (LoadError)
    from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
    from /home/sina/bin/kindle/lib/kindle/note.rb:2:in `<top (required)>'
    from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
    from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
    from /home/sina/bin/kindle/lib/kindle.rb:5:in `<top (required)>'
    from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
    from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
    from ./to_orgmode.rb:3:in `<main>'

I have no knowlege of Ruby. Please help me.