XLVIII. R. T. McKAY, 
Influences affecting run-off.—The proportion of rainfall 
discharged by a stream varies according to the character 
of the catchment, whether it is mountainous, undulating 
or flat, the perviousness or imperviousness of the basin ; 
the quantity and rate of rainfall and its distribution; the 
general geological formation of the country ; atmospheric 
conditions; seepage, etc. The physical conditions affecting 
the run-off are so various, that it is impossible to formulate 
an even approximately correct rule as to the percentage 
of rainfall discharged from a gathering ground. 
In accordance with the principle enunciated by Professor 
Gregory,’ it is noticed that the interior of Australia 
receives most of its rain in summer, for then the currents 
of moist air are moving inland from the ocean. In winter, 
the conditions are reversed, for then the currents proceed 
from the interior to the coast and the air will be passing 
from a warmer to a colder area, thus causing its moisture 
to be condensed. 
In a paper on ‘* The cause of Rain, and the Structure of 
the Universe,’’ Mr. Franz A. Velschow,’ says :— 
“That while the surface air is dry generally, we find it moister 
over a swampy place, as the sun and the warm and dry air 
which passes over 1t cause a strong evaporation to take place. 
The warm surface air, though expanded by heat, moves over the 
‘Professor J. W. Gregory, D.Sc., F.R.S., The Climate of Australia— 
“Tt is a well known fact that water has a higher specific heat 
than land; that is, it requires more heat (the ratio is 5 to 1) to 
raise one pound of water one degree in temperature than to effect 
the same change in one pound of earth. Moreover, while water 
is more slowly heated on exposure to the sun, it gives off its heat 
more slowly. Thus, in the case of equal areas of land and water, 
each receiving precisely the same amount of heat from the sun, 
the land becomes the hotter during the day time, and cools the 
more quickly at night. As in the summer the days are longer 
than the nights, it follows that land will, on the whole, be warmer 
in summer and colder in winter than water adjacent to it.” 
? Trans. Am. Soc. Civil Eng., Vol. xxx111., 1890 
