They were nodding and smiling in unison, and the woman stroked her hair and briefly licked her lips — positive signs of chemistry that would be duly recorded in this experiment at the new eHarmony Labs here. By comparing these results with the couple's answers to hundreds of other questions, the researchers hoped to draw closer to a new and extremely lucrative grail — making the right match. Once upon a time, finding a mate was considered too important to be entrusted to people under the influence of raging hormones. Their parents, sometimes assisted by astrologers and matchmakers, supervised courtship until customs changed in the West because of what was called the Romeo and Juliet revolution. Grown-ups, leave the kids alone. But now some social scientists have rediscovered the appeal of adult supervision — provided the adults have doctorates and vast caches of psychometric data. Online matchmaking has become a boom industry as rival scientists test their algorithms for finding love. The leading yenta is eHarmony, which pioneered the don't-try-this-yourself approach eight years ago by refusing to let its online customers browse for their own dates. It requires them to answer a 258-question personality test and then picks potential partners. The company estimates, based on a national Harris survey it commissioned, that its matchmaking was responsible for about 2 percent of the marriages in America last year, nearly 120 weddings a day.