Book excerpt: Humphry Davy's contemporaries bestowed on him their highest honors. Since Davy's death in 1829, each scholarly generation has accrued info. about him & his colleagues. His startling discoveries of the scientifically novel, his isolation & identification of 7 new elements, & his association of electrical properties & chemical behavior coupled with his fame as a lecturer, made him a popular cultural hero. Others saw him as the man who had made agriculture "scientific." Davy's refusal to profit financially from his invention of the miners' safety lamp endeared him to those humanitarians who idealized scientists as members of an altruistic brotherhood. Here is a readable, thoroughly researched biography of Davy's early life. Illus.