jquery - Why doesn't height reset -

i trying use jquery reset value of height table, in following #expandgrid_header table , #maincontent_expandgrid table

        $("#expandgrid_header").css("height", $("#maincontent_expandgrid tr:nth-child(1)").css("height"));         alert($("#expandgrid_header").css("height") + " __ " + $("#maincontent_expandgrid tr:nth-child(1)").css("height")); 

the following comes out in alert

59px __ 25px 

but trying 25px __ 25px

the following css have on first table

#expandgrid_header      {         visibility: hidden;     } 

and following html

                <table id="expandgrid_header" style="border: 1px solid;">                     <tbody>                         <tr>                             <td>attribute 1</td>                             <td>attribute 2</td>                             <td>attribute 3</td>                             <td>attribute 4</td>                             <td>attribute 5</td>                             <td>attribute 6</td>                             <td>attribute 7</td>                             <td>attribute 8</td>                         </tr>                     </tbody>                 </table> 

you try setting height height() function instead of css value.

$("#expandgrid_header").height($("#maincontent_expandgrid tr:nth-child(1)").height());  alert($("#expandgrid_header").height() + " __ " + $("#maincontent_expandgrid tr:nth-child(1)").height());