FORCING AN APACHE WEB SERVER RETURN A HTTPS HEADER INSTEAD OF HTTP

1-One possible scenario is that we have an index.html in a directory
that is using a frameset : 
<FRAME src="https://........./first_page_user_sees.html">
 
2- What we want to do is to make the web server return a https header to the
browser if the browser makes a valid request (not a 403 - Page Not Found).

To do this, we need to modify the .htaccess file as follows: 

a- add a blank line at end of the .htaccess file
b- and insert 3 lines as follows: 

RewriteEngine on
RewriteCond %{SERVER_PORT}      !^443$
RewriteRule ^(.*)$                      https://........../first_page_user_sees.html [L,R]