MAlfcTl 1, 1895.] 



SCIENCE. 



227 



His mt'tluxl has been to compare the meas- 

 urements of all children of a certain age at- 

 tending various grades of schools. He found 

 that those in the lower grades were inferior 

 in their measurements to those attending 

 the higher grades. He expresses this result 

 in the following language (No. 1, p. 168): 

 " Precocious children are heavier, and dull 

 children lighter, than the mean child of the 

 same age. This establishes a basis of pre- 

 cocity and dullness."' I believe that the 

 method of investigating this point is not 

 free of objections. It would, indeed, be a 

 serious accusation against the tea<,'hers of 

 St. Louis if they should entirely disregard 

 the effects of physical development in grad- 

 ing their pupils. However crudely this 

 may be done, it is certainly done to a lim- 

 ited extent. Sickly children who stay out 

 of school for a gi-eat portion of the term 

 will lag behind ; vigoi-ous ones will advance 

 more rapidly. Be this the case or not, the 

 fact remains that children who are physic- 

 allj' more vigorous accomplish a greater 

 amount of mental work. But I do not be- 

 lieve that Dr. Porter's wording of the phe- 

 nomenon conveys the correct interpreta- 

 tion. I should prefer to call the less favor- 

 ably developed grade of children retarded, 

 not dull ; and these terms are bj- no means 

 equivalent, as a retarded child may develop 

 and become quite bright. In fact, an inves- 

 tig-.ition which I had carried on in Toronto 

 witli the same object in view, but according 

 to a different method, gives just the reverse 

 result. The data were compiled by Dr. G. 

 M. West, who found that the children pro- 

 nounced by the teacher as bright wei"e less 

 favoral)ly developed tluin those called dull 

 by their teachers. Furthermore, I do not 

 believe it is correct to say that the facts 

 found by Dr. Porter establish a basis of pre- 

 cocity and dullness, but only that preco- 

 cious children are at the same time better 

 developed physically ; that is to say, the in- 

 teresting facts presented by Dr. Porter prove 



only that children of the same age who 

 are found in higher grades are more ad- 

 vanced in their general development than 

 those who are found in lower grades. Dr. 

 Porter has shown that mental and physical 

 gi'owth are correlated, or depend upon com- 

 mon causes ; not that mental development 

 depends upon physical growth. 



This brings me back to the question of 

 the cause of the asymmetries of the obsei-ved 

 curves. According to the above interpreta- 

 tion of Dr. Porter's results (which is merely 

 a statement of the observed facts), we 

 must expect to find children of a certain 

 age to be on ditt'erent stages of development. 

 Some will stand on tlie point corresponding 

 exactly to the age. while others deviate from 

 it. This was the assumption which I made 

 in the paper quoted above, when trying to 

 explain the asymmetries of the curves, and 

 I consider Dr. Porter's observations a very 

 strong argument in favor of my theory, 

 which is briefly as follows : 



When we consider children of a certain 

 age we may say that they will not all be on 

 the same stage of development. Some will 

 have reached a point just corresponding to 

 their age, while others will be a little behind, 

 and still others in advance of their age. Con- 

 sequently the values of their measurements 

 will not exactlj- correspond to those of their 

 age. We may assume that the difference 

 between their stage of development and 

 that belonging to their exact age is due to 

 accidental causes, so that just as many 

 will be less developed as further developed 

 than the average child of a particular age. 

 Or, there will be as many children on a 

 stage of development corresponding to that 

 of their age plus a certain length of time 

 as corresponding to that of their age minus 

 a certain length of time. 



The number of children who have a cer- 

 tain amount of deviation in time may be 

 assumed to be arranged in a probability 

 cui've, so that the average of all the ehil- 



