To continue my series of reviews for The World Year of Physics, here's one that addresses the challenging issue of conscience.

In Hitler's Scientists: Science, War and the Devil's Pact, as in his bestselling Hitler's Pope before it, John Cornwell plumbs the history of Nazism for lessons that apply to critical concerns of the present. Once again, his insights are as unsettling are they are revelatory.

Mr. Cornwell presents compelling, detailed life stories of several German scientists, juxtaposing their accomplishments against the political and social turmoil of two world wars, anti-Semitism, Adolf Hitler, and the National Socialist Party.

Among them is the renowned chemist Fritz Haber, who converted from Judaism to Lutheranism "to evade associations that could blight the prospects of a scientist's, or any high official's, career in Germany at that time." Enthusiastically patriotic, though too old for active duty and ineligible for a reserve commission because of his Jewish ancestry, Haber nevertheless became a leader in the German development and use of poison gas during World War I. He later rose to leadership in both research and industry — but to Hitler, he was an expendable Jew.

The story of Werner Heisenberg is powerfully ambiguous. Although never a member of the Nazi Party, Heisenberg led the German effort to develop the atomic bomb. He and other leading German atomic scientists, while detained together in England after the war, carefully constructed a shared myth. They transformed their technological failure into deliberate action, claiming the mantle of moral superiority for choosing not to unleash the evil weapon.

Wernher von Braun's claim to be apolitical fares no better under Mr. Cornwell's sharp research lens and pen. Yet he, like most scientists in the book, is not evil. Rather, each one is remarkably human. Even in the insidious step-by-step march from eugenics to The Final Solution, the choices made by individual scientists are unsurprising. Those are the small details from which the devil's pact of the subtitle arises. Those actions of indifference and self-interest transformed independent individuals into enablers of evil.

In the end, Mr. Cornwell asks, "Will scientists today, in an increasingly crisis-ridden world, in which they are ever more dependent on paymasters to pursue their vocations, behave like the fellow travelers under Hitler...?" Or will their actions be based on a "highly developed grasp of politics and ethics"?

"The best defence against the prostitution and abuse of science," he argues, is to be, in the words of Joseph Rotblat, "human beings first and scientists second." Given the all too human failings of the scientists he describes, some readers may wonder whether, despite Mr. Cornwell's exhortations, scientists in the twenty-first century will act with any more enlightenment than the title scientists of his book.

Dr. Fred Bortz is the author of numerous science books for young readers.