_Frequency of occurrence_. Just how often does a child testing above 180 IQ (S-B) appear in the juvenile population of the United States? We cannot tell exactly until we know more about the spread of the distribution of IQ (S-B). In terms of PE (1 PE = ±8 IQ), according to Terman's original findings (24) we should come upon a deviate of +10 PE only once in more than a million times, provided the distribution of IQ corresponds exactly or even rather closely to Quetelet's (17) curve of probability as respects spread; for on this curve cases above or below ±5 PE approach zero in frequency. It is certain, however, even from existing data, that the distribution of IQ extends for at least ±10 PE (even assuming that wider data will define 1 PE as ±10 instead of ±8 as found by Terman. It is probable that children who test above 180 IQ are actually present in our juvenile population in greater frequency than at the rate of one in a million. This does not mean that intellect when finally measured _in true units_ may not conform in variability to the mathematics of chance; it means only _in terms of IQ_ (in terms of ratio and not of absolute units) the conformity is probably not exact, as respects the law of deviation. There may be one, or two, or three, or more children among every million born in the United States under present conditions who test at or above 180 IQ (S-B). In any case, however, they are extremely rare, and the study of their origin and development is of correspondingly great interest. In the course of discovering about 1000 children testing at or above 140 IQ (S-B) in the state of California, Terman (26) found 15 who tested at or above 180 IQ (S-B). Children who test at and above 140 IQ (S-B) are as 1 in 250 of children in large California cities and environs. Thus 140 IQ (S-B) defines a frequency of about 4 in 1000 of urban juvenile population in California. About 1.5 per cent, therefore, of those children who are as 4 in 1000 reach the status of which we are here treating; i.e., 180 IQ (S-B). [1] Nor can we take the children of California urban districts as a true sample of the population of the United States at large, since there is reason to believe that among urban children there is an uncommon proportion of intelligent individuals (8). Also it should be conceded that California has a total population that is above the average of the United States in general as regards mental ability (37). In any case, it may be guessed with some degree of approximation to fact how very few there are among American children who test at or above 180 IQ (S-B). CHILDREN OBSERVED BEFORE THE ERA OF BINET Scattered observations of children estimated by more or less competent persons as very unusual are to be found dating from quite early years. In this period the literature of child psychology was still in the state of narrative. The earliest of these narrations bears the date of 1726 (1) and concerns the child Heineken.