EMPIRICAL KNOWLEDGE

The "substitution law" is such an accurate empirical law. Origi-nally discovered in 1971 by two General Electric engineers study-ing the market substitution of new products and technology for old, it said (let me use my own words) that the fraction of the new (F) divided by the fraction of the old (1--F) plots against time as a straight line on semilogarithmic paper. Prof. Cesare Marchetti of the Interntl. Inst. of Appl. Systems Analysis has spent years testing the law against other processes, chiefly the substitution of new energy forms, and as often illustrated in these pages, the accuracy of the law is stunning: the transition to oil, for example, cares little about such trifles as two World Wars or an Arab oil embargo.

The curve of total energy consumption does not follow a law as accurately. It lies close to the same type of curve ("logistic" or "learning"), but as Marchetti noted, deviates from it in regular cy-cles reminiscent of Kondratieff's 55-year business cycles. Mar-chetti attributes the cycles to innovations (industry-founding ones like automobiles or computers). The deviations are barely visible on a logarithmic scale, but are very clear on the linear plot:

The figures illustrating this behavior are taken from a book to be published this fall, Recollecting the Future by H. B. Stewart (Dow Jones-Irwin). A summary appears in the Summer 1988 Gas-Cooled Reactor Associates Newsletter (10240 Sorrento Valley Rd., San Diego, CA 92121).

From the reliability of the "postdictions" it seems certain that an energy spring will start around 1995, with US energy consumption doubling by 2020, reaching 140 quads, with 50% of it going into electricity generation.