A little more interesting demonstration
The first applet:

The second applet:

These two applets are driving each other crazy. After you press the button above, the first applet started counting down. When it is 5 seconds from timeup, it will send a message. The second applet receives the message and display "ready". When the first applet is timeup, the second applet starts.

You understand this?
For those who accessed this page before 2nd September 1997 4:30 pm Eastern Australia time, this page only works for IE and causes an error for Netscape. It is due to the applets are placed inside the form which hosts the button.
For Internet Explorer, the applet inside a form is referred to as
document.formname.appletname.
whereas for Netscape, it is just
document.appletname

The current implementation moves the two applets outside of the form.

The inconsistency of the object model for the two browsers caused this problem. And I am to blame for not testing it properly! Thank you Kin Leung for pointing this out to me.