It's a clichÇ that more scientists are alive today than in all of previous history. Regardless of numbers, science as we know it began in earnest when one idea led to another in an inexorable chain; a good argument can be made that the 18th century was pivotal, with astronomers Halley and the brother- sister team of William and Caroline Herschel; chemists such as Lavoisier, Priestly, and Cavendish; and biologist Carl Linnaeus. Americans, too, made their mark, with Franklin and the astonishing scoundrel Count Rumford, ``father of thermodynamics.'' Covering both physical and life sciences, the authors trace the sometimes tortuous path of reasoning that underlies present scientific understanding, in the process uncovering some intriguing frailties of early scientists—e.g., the royalist Lavoisier (later guillotined) was so affronted by Priestly's liberal leanings that he avoided crediting him with key discoveries. People come across more vividly than science in this title in the ``On the Shoulders of Giants'' series, but the writing is lively and engaging. Appendix on the scientific method; chronology; glossary; extensive annotated bibliography. Illustrations and index not seen. (Nonfiction. 13+)