Man has been storing up useful knowledge about himself and the universe at the rate which has been spiraling upward for 10,000 years.
　　The (21) took a sharp upward leap with the invention of writing, but even (22) it remained painfully slow for several centuries. The next great leap forward (23) knowledge acquisition did not occur (24) the invention of movable type in the 15th century by Gutenberg and others. (25) to 1500, by the most optimistic (26) Europe was producing books at a rate of 1000 titles per year. This means that it (27) a full century to produce a library of 100,000 titles. By 1950, four and a half (28) later, the rate had accelerated so sharply that Europe was producing 120,000 titles a year. (29) once took a century now took only ten months. By 1960, a (30) decade later, the rate had made another significant jump, (31) a century’s work could be finished in seven and a half months. (32) , by the mid-sixties, the output of books on a world (33) , Europe included, approached the prodigious figure of 900 titles per day.
　　One can (34) argue that every book is a net gain for the advancement of knowledge. Nevertheless we find that the accelerative (35) in book publication does, in fact, crudely (36) the rate at which man discovered new knowledge. For example, prior to Gutenberg (37) 11 chemical elements were known. Antimony the 12th, was discovered (38) about the time he was working on his invention. It was fully 200 years since the 11th, arsenic, had been discovered. (39) the same rate of discovery continued, we would by now have added only two or three additional elements to the periodic table since Gutenberg. (40) , in the 450 years after his time, certain people discovered some seventy additional elements. And since 1900 we have been isolating the remaining elements not at a rate of one every two centuries, but of one every three years.

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