There are two different download simulations in this forum:
1. Under JDK1.0.2 simulations (1996-2001): Those simulations are created before 2001. The download ZIP file contain java class file and html files. You need to unzip the file and view the html file (normally, xxx.html where xxx is the same as the downloaded zip file.
2. EJS simulatoions: Those are simulations created with EJS. The download file is a jar file. You can dooble click the jar file to run it. You can open it with EJS when right click the mouse button and select open ejs model option. There are many other options.

The above message are include in the email message you received when you request our server sent you file.

The simulation for this topic is a thin lens. It means that the width of the lens is ignored and approximation has been made. That is why you did not find double refraction for a ray pass through the center. You can find more accurate rar tracing from simulations for [url=http://thick lens]thick lens[/url] .