The phrase to be on cloud nine, meaning that one was blissfully happy, started life in the United States and has been widely known there since the 1950s; it’s since spread worldwide. It’s said to have been popularised by the Johnny Dollar radio show of that period, in which every time the hero was knocked unconscious he was transported to Cloud Nine. But that wasn’t the origin of the phrase. It’s been around since the 1930s, though early examples show a lot of numerical variability, with the cloud sometimes being as low as number seven or eight or as high as thirty-nine, though seven and nine were most common.

These discrepancies make me suspect the usual explanation of its origin, which is that it comes from the US Weather Bureau. The story is that this organisation describes (or once described) clouds by an arithmetic sequence. Level Nine was the very highest cumulonimbus, which can reach 30,000 or 40,000 feet and appear as glorious white mountains in the sky. So if you were on cloud nine you were at the very peak of existence.

The term has always had close associations with the euphoria that is induced by certain chemicals — alcohol in its earlier days but more recently crack cocaine — so perhaps we shouldn’t ask for too great a level of exactness in counting. And the cloud here is an obvious reference to some drug-induced dreamy floating sensation. But I suspect, without having anything so restricting as evidence, that seven was chosen because it’s a traditional lucky number and that today’s more usual nine appears for similar reasons — for example it also turns up in dressed to the nines and the whole nine yards.