Get Value of Radio button group

I'm trying to get the value of two radio button groups using the jQuery syntax as given below. When the code below is run I get the value selected from the first radio button group twice instead of getting the value of each individual group.

Am I doing something obviously wrong here? Thanks for any help :)

<a href='#' id='check_var'>Check values</a><br/><br/>
<script>
  $('a#check_var').click(function() {
    alert($("input:radio['name=r']:checked").val()+ ' ' +
          $("input:radio['name=s']:checked").val());
  });
</script>
Group 1<br/>
<input type="radio"  name="r" value="radio1"/> radio1
<input type="radio"  name="r" value="radio2"/> radio2
<br/><br/>
Group 2<br/>
<input type="radio"  name="s" value="radio3"/> radio3
<input type="radio"  name="s" value="radio4"/> radio4