function validate() {
if (document.getElementById("callback").name.value == "" ){
  alert("Please enter a name");
  return false;
  }

else if (document.getElementById("callback").company.value == "" ) {
  alert("Please enter a company name");
  return false;
  	}
	
else if (document.getElementById("callback").phone.value == "" ) {
  alert("Please enter an telephone number");
  return false;
  	}
	
else if (document.getElementById("callback").captchacode.value == "" ) {
  alert("Please enter the authentication digits");
  return false;
  	}
  
 else {
 return true;
 }
 
}