THE utility of biography, Dr. Johnson argued, rests on the fact that we can enter by sympathy into situations in which others have found themselves. Parallel circumstances to which we can conform our minds shape every life. Even the great are not removed from the factors common to all: “We are all prompted by the same motives, all deceived by the same fallacies, all animated by hope, obstructed by danger, entangled by desire, and seduced by pleasure.” I must confess that twenty years devoted to the biography of Newton have not in my case confirmed Dr. Johnson's dictum. The more I have studied him, the more Newton has receded from me. It has been my privilege at various times to know a number of brilliant men, men whom I acknowledge without hesitation to be my intellectual superiors. I have never, however, met one against whom I was unwilling to measure myself, so that it seemed reasonable to say that 1 was half as able as the person in question, or a third or a fourth, but in every case a finite fraction. The end result of my study of Newton has served to convince me that with him there is no measure. He has become for me wholly other, one of the tiny handful of supreme geniuses who have shaped the categories of the human intellect, a man not finally reducible to the criteria by which we comprehend our fellow beings, those parallel circumstances of Dr. Johnson.