TUVA OR BUST! Richard Feynman's Last Journey By Ralph Leighton (Penguin, $102) RICHARD Feynman was for many years one of America's leading theoretical physicists - distinguished teacher, Nobel laureate wonderchild of the Manhattan Project and so on. Happily, though, he resisted the temptations of pomposity and remained a man of boundless curiosity and subtle humour. This side of his character produced two wonderful collections of autobiographical fragments - both with Mr Leighton - called Surely You're Joking, Mr Feynman and What Do You Care What Other People Think!. Mr Leighton flies solo in this last volume because Feynman died in 1988. Clearly his friends miss him still and so, I imagine, do many readers. The story starts in 1977, with the simple question: ''Whatever happened to Tannu Tuva?'' The sole claim to fame of this short-lived country is that it used to issue stunning stamps before it was gobbled by Stalin. Having sorted out that such a place did exist, it was decided that it deserved a visit. This was not as easy as you might think. Tuva is a sliver of territory in Russian Siberia just north of Mongolia. The easiest solution would have been for Feynman to pull scientific strings, but that would be cheating. So this book chronicles 10 years of trying to get to Tuva the hard way. The result is an odd piece of work. It isn't really biography, history, geography or politics. It certainly isn't academic. It is what it is: three lively minds having fun with an intricate practical problem.