From the primitive experiments of Copernicus in the 15th century to those of radio astronomers Smith and Bande in the early 1950's, the author devotes a chapter each to the discoverers and innovators of astronomy. The most often written about at the juvenile level are Kepler, Galileo and Newton and they are, of course, here. The real service of the book is the steady progress of events to the 19th and 20th century astronomers whose names and work are less familiar: Adams and Leverrier using Newton's law of gravity to discover Neptune in the 1840's; Huggins pioneering in the use of photography and spectrum analysis in the 1870's; Hubble and Tansky complementing each others' discoveries of an expanding universe in the 1930's. Mr. Sullivan's method is essentially the same one he employed in Pioneer Germ Killers (1962, 687, J-207). He makes a clear statement of the problem each man investigates, he shows the cooperation among the scientists working in allied areas and he details the way the conclusive experiment is arrived at. The use of exclamatory dialogue is occasionally intrusive but, more often than not, the dialogue is effective.