Working with for loop in Jquery

Working with for loop in Jquery

I want to use for loop in JQuery.Recently am using this
var os= $tr.find("td:eq(1)").html();
But putting inside for loop it alerts undefined value
var i;
for(i=0; i<3; i++) {
var os= $tr.find("td:eq('+i+')").html();
alert("os----------------------"+os)
}