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XXVI BUREAU OF AMERICAN ETHNOLOGY 
of investigation relate to (1) Arts or esthetology, (2) Industries 
or technology (including archeology), (3) Institutions or soci- 
ology, (4) Languages or philology, and (5) Myths and opinions 
or sophiology, as well as the requisite classificatory work involv- 
ing researches in somatology and psychology. 
The end of research in the Bureau of American Ethnology is 
the discovery of the relations of the aboriginal American tribes 
among each other and among the peoples of the world. The 
simpler relations are ascertained by direct observation and 
defined by the aid of generalization; and continued observa- 
tion and generalization have led to the establishment of prin- 
ciples which aid in defining the more complex relations. The 
salient principles developed through the researches have been 
set forth in previous reports; they serve to define the general 
science of man, to distinguish the essentially human charac- 
teristics from those of the lower animals, and to outline the 
primary categories of activities which characterize mankind. 
The recognition of the essentially human activities affords a 
means for classifying tribes and peoples. The classification in 
terms of activities represents a decided advance beyond the 
plane of classification in terms of physical characteristics, and 
raises the science of man to the level of the older sciences 
in their modern aspects—e. g., to the plane occupied during 
recent years by physical astronomy or physical geology. At 
the same time the classification leads to the recognition of the 
lines of human development, and serves to define their trend; 
and thereby it prepares the way to clear comprehension and 
accurate definition of the natural stages in human develop- 
ment, i. e., the four principal culture grades. Since each new 
recognition of relation extends the view of the student, the 
definition of the culture grades reacts on knowledge of the 
primary activities, and conduces to still more accurate and 
extended survey of the course of activital growth. 
The lines of development discerned among the American 
aborigines were set forth in terms of the activities in the last 
report; it was there shown that in each of the five categories 
the activities developed along convergent lines. For the pres- 
