Winston Churchill, whose output as a writer was so prodigious that one might reasonably wonder whether he was paid by the page, was him- self put off by long works. As prime minister of Great Britain, he once pushed away a report from a junior minister, observing, "This paper, by its very length, defends itself against the risk of being read." No doubt some laymen will glance at the study that follows and be deterred from further consideration by the fact that the study is a scien- tific one. If that is a hurdle for you, I hope you will join me in getting over it, because, if you do, you will...