如何访问 jQuery 中的列

$('td').each(function(){
  console.log($(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>