What a splendid fellow was Quintus Septimus Tertull ianus. If someone were to ask you, for example, who first said, "See how these Christians love one another", you would probably think, as I did, that it was Shylock in The Merchant of Venice. But no! What he said was:
O father Abram, what these Christians are,
Whose own hard dealings teaches them suspect
The thoughts of others.
Tertullian coined the other phrase in Apologeticus.
Himself a Christian and a priest of the strictest, most unforgiving kind, Tertullian lived in the second century AD, and had a knack with little mots like this that were to last in perpetuity. His most celebrated soundbite legacy is de calcaria in carbonarium, which first appeared in De Carne Christi, "On the Flesh of Christ"; it means, as the old music-hall song has it, "Out of the frying pan, into the blooming fire".
Imagine yourself about to fry a sausage on the barbecue, and imagine also the first drops of the inevitable rain landing on the hot, but as yet empty, frying pan. It is interesting to observe how they behave.
If the surface of the pan is fairly hot, say 150 to 200 Celsius, the drops will evaporate very quickly and disappear immediately in a little whiff of steam - which, I suppose, is precisely what you would expect.
But if the pan is very hot, hotter than about 350 Celsius, a strange thing happens: the drops of water glide serenely and gracefully around the pan, and do not evaporate for several minutes more.
This is because the drops have acquired a little cushion of water vapour to hold them a fraction of a millimetre above the surface of the pan. This insulating cushion only forms when the surface of the pan is very hot indeed, but when it does materialise it acts as an insulator to prevent the heat flowing freely upwards into the liquid drop of water.
The raindrops skim like tiny skaters round and round the frying pan, their longevity assured by the frictionless cushion on which each one is perched.
The most spectacular events occur, however, if the pan is at a temperature that is intermediate between these two extremes. The raindrops then have difficulty in deciding whether they have landed on a merely warm pan or a very hot one, and they rapidly alternate between making contact with the surface and bouncing into the air.
They strike the surface perhaps 20 or 30 times a second, and with each bounce a multitude of very tiny droplets is sprayed upwards to the accompaniment of the familiar sizzling sound.