James B. Conant, who is one of the country's most eminent scientists as well as one of its most notable practitioners of education, tells here how he believes the layman can find out what science is and how to understand it.  The language, customs, and manners of the scientists are frequently unintelligible to the rest of the population, and there is considerable danger that the ideas and forces that are moving mountains will be increasingly inaccessible to those outside the laboratories.  The peril of such a situation to a democracy, where understanding must be assumed to be fairly general, is probably as great in the realm of ideas as the physical danger of the instruments of destruction.  Dr. Conant sets out to show how the gulf can be bridged.  Instead of a series of assertions about science being ordered knowledge, or the classification of facts, he presents a historical view of a number of the great scientists, of what their generation knew of their subjects, of the problem they set out to examine, and of how they solved it.  Thus the reader is enabled to follow in a new way the scientific method at work, with all its limitations and wonders.