Icelandic happiness is even more of a mystery than Swiss bliss. Iceland is cold and dark for much of the year. It is isolated and, for goodness sake, has the word ice in its name. Not much happy about that, yet these descendants of the Vikings are, statistically, among the planet’s happiest people. It turns out that Icelanders know a thing or two about the art of contentment. They know, as researchers have discovered, that much of our happiness is derived from our relations with others. Icelanders are a close-knit bunch. They are, virtually, one big family. Genealogists have determined that nearly all Icelanders are related, going back seven or eight generations, and family is one of our greatest sources of happiness. Icelanders also derive much pleasure from their creative streak. For a tiny country with a population roughly the size of Louisville, Ky., Iceland churns out an exceptionally large number of world-class artists and musicians (Björk being only the best known). And Iceland publishes more books, per capita, than any other country. ‘‘Better to go barefoot than to go without books,’’ is a well-known Icelandic expression.