Causes for this influx are varied.
"History of the United States, Volume 6 (of 6)"
E. Benjamin Andrews
The earth's loss of heat by radiation goes on ceaselessly day and night, and were it not for the influx of solar heat this radiation would steadily diminish the temperature toward what is called the "absolute zero"-i.
"A Text-Book of Astronomy"
George C. Comstock
This was the more striking because there was at the same time an influx more than enough to repair the loss from leakage.
"Wild Life in a Southern County"
Richard Jefferies