JQuery循环滚动图片代码

function refresh() { 
var s = $(".box1"); 
if (!s.is(":animated")) 
$(".box1").animate({ marginLeft: "0px" }, "slow", function () { 
$('.box1 img:first').before($('.box1 img:last')); 
$(".box1").css("margin-left", "-206px"); 
}); 
} 
<div class="frame"><div class="box1"><img src="img/001.png" alt="" /><img src="img/002.png" alt="" /><img src="img/003.png" alt="" /><img src="img/004.png" alt="" /></div></div> 
<button type="button"><<</button><button type="button" onclick="refresh()">>></button> 
.box1 
{ 
width:1200px; 
overflow:hidden; 
margin-left:-206px; 
} 
.frame 
{ 
width:620px; 
overflow:hidden; 
}

图片宽度默认206px，没设定