Febeuaby 4, 1910] 



SCIENCE 



171 



light sources taken from Professor Lang- 

 ley's work (Fig. 4). The difficulties at- 

 tendant upon the accurate determination 

 of the curve for the fire-fly are so great 

 that we ought not to expect very great ac- 

 curacy in this case. These curves, which 

 in each case refer to the energy after pass- 



ing through glass, which cuts off energy of 

 long wave-lengths, represent the same 

 quantities of radiant energy. While the 

 sun is much more efficient than the gas 

 flame or carbon arc, it still presents far 

 the largest part of its energy in the invis- 

 ible long wave-lengths (above 0.8), while 

 the fire-fly seems to have its radiant energy 

 confined to a narrow part of the visible 

 spectrum. 



W. R. Whitney 

 Geneeal Electeic Company, 

 schenectadt, n. y. 



RACIAL DIFFERENCES IN MENTAL TRAITS' 

 One of the most agreeable and satisfying 

 experiences affiorded by intellectual pur- 

 suits comes from the discovery of a clean- 

 cut distinction between things which are 

 superficially much alike. The esthetic 

 value of such distinctions may even out- 

 weigh their intellectual value and lead to 



'Address of the vice-president and chairman of 

 Section H — Anthropology and Psychology — of the 

 American Association for the Advancement of 

 Science, Boston, 1909. 



sharp lines and antitheses where the only 

 difl:erence that exists is one of degree. 

 A favorite opportunity for this form of 

 intellectual exercise and indulgence is af- 

 forded by the observation of groups of 

 men. The type of man composing each 

 group— that is what we should like to find; 

 and we hear much of the "typical" scien- 

 tist, the typical business man, the typical 

 Englishman or Frenchman, the typical 

 southerner, the typical Bostonian. The 

 type of any group stands as a sort of ideal 

 within the group, and, more or less cari- 

 catured, as the butt of the wit of other 

 groups. There is one peculiar fact about 

 these types: you may have to search long 

 for an individual who can be taken as a 

 fair example. And when you have at last 

 found the typical individual, you may be 

 led to ask by what right he stands as the 

 type of the group, if he is a rarity amidst it. 

 If we would scientifically determine the 

 facts regarding a group of men, we should, 

 no doubt, proceed to examine all the indi- 

 viduals in the group, or at least a fair and 

 honest representation of them. The first 

 fact that meets us when we proceed in this 

 way is that the individuals difl'er from each 

 other, so that no one can really be selected 

 as representing the whole number. We do 

 find, indeed, when we measure the stature 

 or any other bodily fact, or when we test 

 any native mental capacity, that the mem- 

 bers of a natural group are disposed about 

 an average, many of them lying near the 

 average, and few lying far above or far 

 below it; and we thus have the average as 

 a scientific fact regarding the group. But 

 the average does not generally coincide 

 with the type, as previously conceived, nor 

 do the averages of different groups differ 

 so much as the so-called types differ. 

 Moreover, the average is itself very inade- 

 quate, since it does not indicate the amount 

 of variation that exists within the group — 



