It's said that the martini was invented 140 years ago by Professor Jerry Thomas, bartender at the Occidental Hotel on Montgomery Street. The Savoy Cocktail Book called Thomas "the greatest bartender of the past," although contemporary accounts indicate that his martini was made up of half gin and half sweet vermouth, an appalling thing to contemplate. The real deal -- the elusive, almost vaporous transcendence we have evolved enough to appreciate -- is shaken and proffered with admirable artistry at Maxfield's, a couple of blocks south of the cocktail's presumed birthplace. It's a chillingly cold elixir, this martini, barely kissed with vermouth, juniper edge softened through a rhythmic intermarriage with ice. (Yes, juniper. A martini is made with gin, not vodka or tequila or Bosco, because only the therapeutic properties of this aromatic base can cushion the soul and lighten the heart with such liquid equanimity.) Maxfield's itself is a time-honored San Francisco classic (45 years ago Esquire named it one of the seven greatest bars in the world) renowned for the original Maxfield Parrish mural behind the bar and the surrounding opulence of the Palace Hotel.