why this doesn't work as an external file but does internally?

Hi guys, I have this code Javascript code: if (document.images) { img1on = new Image(); img1on.src = "<?php echo $base_url; ?>Graphics/<?php echo $img_home_on; ?>"; img2on = new Image(); img2on.src = "<?php echo $base_url; ?>Graphics/<?php echo $img_programdetails_on; ?>"; img3on = new Image(); img3on.src = "<?php echo $base_url; ?>Graphics/<?php echo $img_products_on; ?>"; img4on = new Image(); img4on.src = "<?php echo $base_url; ?>Graphics/<?php echo $img_featuredproducts_on; ?>"; img5on = new Image(); img5on.src = "<?php echo $base_url; ?>Graphics/<?php echo $img_faq_on; ?>"; img6on = new Image(); img6on.src = "<?php echo $base_url; ?>Graphics/<?php echo $img_contact_on; ?>"; img1off = new Image(); img1off.src = "<?php echo $base_url; ?>Graphics/<?php echo $img_home_off; ?>"; img2off = new Image(); img2off.src = "<?php echo $base_url; ?>Graphics/<?php echo $img_programdetails_off; ?>"; img3off = new Image(); img3off.src = "<?php echo $base_url; ?>Graphics/<?php echo $img_products_off; ?>"; img4off = new Image(); img4off.src = "<?php echo $base_url; ?>Graphics/<?php echo $img_featuredproducts_off; ?>"; img5off = new Image(); img5off.src = "<?php echo $base_url; ?>Graphics/<?php echo $img_faq_off; ?>"; img6off = new Image(); img6off.src = "<?php echo "{$base_url}Graphics/{$img_contact_off}"; ?>"; } When I include it in the main page it works without any problems. When I link it as an external file it doesn't work. As a side note, the following code example works in an external JS file: img1off = new Image(); img1off.src = "<?php echo $base_url; ?>Graphics/home_off.gif"; Anyone know why the external file with two variables is not working but it does work with one variable? Thanks! I appreciate the help! Regards, Aaron