Jacob Bernoulli's most original work was "Ars Conjectandi" published in Basel in 1713, eight years after his death. The work was incomplete at the time of his death but it is still a work of the greatest significance in the theory of probability. In the book Bernoulli reviewed work of others on probability, in particular work by van Schooten, Leibniz, and Prestet. The Bernoulli numbers appear in the book in a discussion of the exponential series. Many examples are given on how much one would expect to win playing various games of chance. The term Bernoulli trial resulted from this work. There are interesting thoughts on what probability really is: