media search for iPad

media search for iPad

I am trying to get the @media search to work but with not success. I am
using the following code but the only image I can displayed is the
headernew.jpg never the headerold.jpg so it seams that none of the media
queries are working. I have tested on a 27in iMac and a iPad but both
display the same background image. Any help would be appreciated.
Thanks Roger
div.art-header-jpeg
{
position: absolute;
top: 0;
left:-50%;
width: 1344px;
height: 150px;
background-image: url('../img/headernew.jpg');
@media only screen and (max-width : 900px){div.art-header-jpg
{background-image: url('../img/headerold.jpg');
}
}
}