как в jQuery обращаться к columns

$('td').each(function(){ 
  console.log($(this).html()); 
  alert($(this).html()); 
});

<script src="https://code.jquery.com/jquery-2.0.3.js"></script> 
   
<table class="employeeTable" border="1"> 
<thead> 
<tr> 
<th class="employeeTableHeader" scope="col">Name</th> 
<th class="employeeTableHeader" scope="col">Department</th> 
<th class="employeeTableHeader" scope="col">Age</th> 
<th class="employeeTableHeader" scope="col">Salary</th> 
</tr> 
</thead> 
<tbody> 
<tr class="employeeTableOddRow"> 
<td>         
            John 
 </td> 
<td> 
            Marketing 
         </td> 
<td> 
 
            30 
         </td> 
<td> 
            2000.0 
         </td> 
</tr> 
<tr class="employeeTableEvenRow"> 
<td>         
            Robert 
 </td> 
<td> 
            Marketing 
         </td> 
<td> 
 
            35 
         </td> 
<td> 
            3000.0 
         </td> 
</tr> 
<tr class="employeeTableOddRow"> 
<td>         
            Mark 
 </td> 
<td> 
            Sales 
         </td> 
<td> 
 
            25 
         </td> 
<td> 
            2500.0 
         </td> 
</tr> 
<tr class="employeeTableEvenRow"> 
<td>         
            Chris 
 </td> 
<td> 
            Marketing 
         </td> 
<td> 
 
            33 
         </td> 
<td> 
            2500.0 
         </td> 
</tr> 
<tr class="employeeTableOddRow"> 
<td>         
            Peter 
 </td> 
<td> 
            Customer Care 
         </td> 
<td> 
 
            20 
         </td> 
<td> 
            1500.0 
         </td> 
</tr> 
</tbody> 
</table>