function volume_sphere()  
 {  
  var volume;  
  var radius = document.getElementById('radius').value;  
  radius = Math.abs(radius);  
  volume = (4/3) * Math.PI * Math.pow(radius, 3);  
  volume = volume.toFixed(4);  
  document.getElementById('volume').value = volume;  
  return false;  
 }   
window.onload = document.getElementById('MyForm').onsubmit = volume_sphere;