If the effect is acceptable, try the following:
$('.div1').show('scale', { direction: "both", duration: 1000 }); $('.div2').hide('scale', { direction: "both", duration: 1000 });
JSFiddle: http://jsfiddle.net/AUM6d/307/
It is a little different, but it works. From my testing (and the jQueryUI demo page) it looks like this: direction: 'horizontal' is an error.
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