Thank you for being on alert and taking the time to inform me of the malfunction.The applet worked fine on all of my computers except one. The difference was that on that one Java3D was missing. All it took was to install Java3D.
Please, google for "Download java 3d". There are several sit's. I went to sun.com. Download Java3d 1.5.1. This is an executable file so that, when asked, you'll have to allow it to run. All in all , it took just 2 minutes.
After the installation. Close all your browser windows. Start a browser again. Go to
https://www.cut-the-knot.org/Curriculum/Geometry/PossibleImpossible.shtml