Please wait a while and try again when the server may not be as busy. As an alternative, you may wish to try one of the following unofficial mirror sites. Please make sure to enter your email address in the preferences as well as other items when you first use Mosaic. However, to view some images, watch movies and listen to sounds, you need to install additional software. The online Macintosh documentation provides pointers to these external viewers.
More information is available online, through the balloon help menu.