[jQuery] Resizing two divs proportionally

[hubbs]

I would like to know how I could resize two divs proportionally to
each other.  I have the resize UI plugin working to resize the top
div, but I would like the bottom div to resize as well, depending on
the resizing of the top div. (Similar to how many mail programs manage
the list of mail, and viewing the mail below that).

I used:
$("#resizebleImage").resizable({
    handles: "s",
    proxy: "proxy"
});

Now, I know there is a UI option called proportionallyResize, but I
can find no info or help about this.