[jQuery] fadein is not a function?

Hi

I'm doing some online tutorials and simple tasks....

I'm getting an error on the function .fadein

can someone please tell me what is wrong with this code.

$(function() { // document is ready for load
$('a').click(function() {
$('.box').fadein(5000);

});
});

Here is the inline style and markup
<style type="text/css">
.box { background-color:blue; width:200px; height:200px; }
</style>

<div id="box"></div>
<a href="#">Click my link</a>

Thanks
Much appreciated.
Jess