Begun in the late 1960s by Pentagon weapons researchers as a system for easing communication between computers in disparate electric networks, the Internet has (1) ______ evolved into a popular vehicle for scientific research, communication, entertainment, and more. It links together thousands of computer networks such as those belonging (2) ______ to corporations, commercial services, universities, and research centers, joining them as branches on a tree to larger networks known as backbones. Once a computer is on-line, that is, connected by modem or networking equipment of the Internet, the user can search (3) ______ through data banks for documents, chat with other computer users, or instant send (4) ______ opinions and observations to the likes of President Bill Clinton, film critic Roger Ebert, or rocker Billy Idol (just to name a few). No central governing body runs the Internet, and nobody has an exact census of users. But estimates of the number already range (5) ______ from around 10 million to as high as 5 million. Well over 10,000 separated computer (6) ______ networks are connected by the Internet, and total traffic was expected to double during 1993. Today, the Internet is free resources and commercial services that provide databases and computer files with a fee. Publishers are seeking to make books and (7) ______ periodicals available on the Internet as a profit-making adventure. Meanwhile, works (8) ______ in the public domain have begun appearing on the Internet for users to "upload" to their (9) ______ computers virtually free of charge. With electronic access to data from all over the world, scholarly research that in the past would have required months of travel could (10) ______ now be done at one’s desk.