(On the temperature of water in wells) The reason why the water in wells becomes colder in summer is that the earth is then rarefied by the heat, and releases into the air all the heat-particles it happens to have. So, the more the earth is drained of heat, the colder becomes the moisture that is concealed in the ground. On the other hand, when all the earth condenses and contracts and congeals with the cold, then, of course, as it contracts, it squeezes out into the wells whatever heat it holds.
Source: Lucretius On the nature of things (De Rerum Natura), Sphere Books, London, 1969
Contributed by: Zaady