I found the answer:
I had to change the CSS (I thought I made a mistake with jQuery)
div.fieldgrid
{
display: inline-block;
width: 20px;
height: 20px;
border: 1px solid blue;
}
div.bar
{
width: 20%;
height: 500px;
border: 1px solid red;
float: left;
}
div.field
{
width: 500px;
height: 500px;
overflow: auto;
overflow-x: scroll;
background-color: #ffffff;
white-space: nowrap;
}