RELATIONS AMONG THE SCIENCES 195 



mineral and agency and a highly effective constituent of the atmosphere ; 

 at least at the oiitset, it would naturally form a branch of the former 

 science, with its organized instrumentalities and institutions. In the 

 general order of sciences running from the simple to tlie complex (astron- 

 omy based on gravity and other mass relations which may collectively be 

 denoted molarity, chemistry based on affinity — or molecularity — plus 

 molarit)', phytology based chiefly on vitality plus affinity and molarity, 

 zoolog}^ based largely on motility plus vitality and affinity and molarity, 

 and anthropology based mainly on mentality plus all the simpler bases), 

 hydrology would occupy an intermediate position, in some measure span- 

 ning the interval between the bases of affinity and vitality — this in ways 

 which can only be suggested now and which must remain for research to 

 elucidate and demonstrate. 



Elements of Hydrology 

 water as a plaxetart coxstituext 



The mineral HjO, forming the hydrosphere, takes a leading role in tlu' 

 play of terrestrial progress: Practically covering the planet, existing in 

 the three states of solid and liquid and vapor under natural temperatures, 

 extraordinarily high in molecular inertia or specific and latent heat, and 

 constantly changing from one state to another with the diurnal and an- 

 nual procession of planetary movement, it is the most effective known 

 agent in determining external terrestrial conditions. Without it, the 

 earth would be lifeless; with its quantity quadrupled, the globe would be 

 iminhabitable by higher life-forms; perhaps decreasing slowly in anion nt 

 and certainly concentrating in deepening seas, it has permitted the growth 

 of continents and the evolution of organisms, now limits the liabita- 

 bility of the one by the other, and with continued diminution threatens 

 organic existence in that the world's deserts are manifestly increasing, 

 though under Chamberlin's planetesimal theory the aggregate volume may 

 be so increasing as to balance the concentration. In its movements and 

 changes of state the leading external agency of earth-making, it first 

 brought forth and then gave form to the continents; and the organisms 

 developed Avithin it to reach higher estate on' land depend on it both for 

 tlie chief part of their substances and for all their vital processes. A 

 growing and living world without water is unthinkable. 



The temperature and climate of the globe are determined by an atmos- 

 pheric mechanism of which the dominant factor is HoO. The aqueous 

 vapor in the atmosphere forms a l)lanket against radiation in wliich the 

 sun heat is both conserved and distributed; when liquefied or solidified 



