[jQuery] New to jQuery: Problem setting current time to some element

[Nazgulled]

Hi,
This is my code:

function displayDate(){
  var date = new Date();
  $("#dateandtime").text(date);
}


$(document).ready(function(){
   setInterval('displayDate()', 1000);
});

But it doesn't work, however, if I have this:
$("#dateandtime").text("some text");

The content of the <span> element with "dateandtime" id selector will
change to "some text". I don't understand why it doesn't change when I
have this:
$("#dateandtime").text(date);

I'm new to jQuery, please advise... Thanks in advance.