In 1920, after failing five times to find a publisher for his newly finished book, Tractatus Logico-Philosophicus, the Austrian-born philosopher Ludwig Wittgenstein consoled himself in a letter to Bertrand Russell:

Either my piece is a work of the highest rank, or it is not a work of the highest rank. In the latter (and more probable) case I myself am in favour of it not being printed. And in the former case it's a matter of indifference whether it's printed twenty or a hundred years sooner or later. After all, who asks whether the Critique of Pure Reason ... was written in 17X or y.

The following year the book finally found a publisher. The 100th anniversary of its publication this year is being celebrated all over the world by exhibitions, conferences, radio programmes and articles, all of which attest to its recognition as "a work of the highest rank".

Despite being one of the most celebrated works of philosophy ever written, the Tractatus is also one of the most gnomic--even now there is no consensus about how it should be interpreted. It has nevertheless exerted a fascination that extends beyond the confines of academic philosophy. Conceptual artists, poets, film-makers and novelists have all cited it as an influence, and it has been set to music by more than one composer. In that respect, the book reflects its charismatic author, who exerted a magnetism over those with whom he came into contact. Russell called him "the most perfect example I have ever known of genius as traditionally conceived, passionate, profound, intense and dominating".

Wittgenstein was born in Vienna in 1889 into immense wealth. His father Karl was an iron and steel magnate, "the Austrian Carnegie". The family owned several homes, including the grand "Palais Wittgenstein" in Vienna. The families of both Karl and his wife Leopoldine had Jewish origins, but by the time Ludwig was born they did not consider themselves Jewish and he was raised a Catholic.

The Wittgensteins were at the heart of Viennese cultural life. Ludwig's sister Margaret was a friend and client--of Sigmund Freud's. His father paid for the Secession Building that exhibited the works of, most notably, Klimt and Schiele. Brahms was a regular visitor to the Wittgenstein Palais, in which a number of his works had their first performance. The standards of musical talent in the family were so high that, although Ludwig's brother Paul became a concert pianist, his playing was considered inferior to that of some of his siblings.

But despite abundant wealth and talent, the family was also marked by tragedy. When Wittgenstein was a young boy, two of his elder brothers, Hans and Rudolf, took their own lives. After these suicides, Karl took a less overbearing attitude to the career choices of his children and Paul was allowed to pursue his musical bent. The sisters, Hermine, Helene and Margaret, too, devoted themselves to music and literature.

Unlike his siblings, Ludwig developed an interest in machinery. At the age of ten,...