One can hardly argue that every book is a net gain for the advancement of knowledge.Nevertheless, we find that the accelerative curve in book publication does, in fact, crudely parallel the rate at which man discovered new knowledge.For example, prior to Gutenberg only 11 chemical elements were known.Antimony the 12th,was discovered at about the time he was workingon his invention.It was fully 200 years since the 11th,arsenic,had been discovered.Had the same rate of discovery continued, we would by now have added only two or three additional elements to the periodic table since Gutenberg.Instead, in the 450 years after his time, some seventy additional elements were discovered.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.