Howard Friedman, a psychologist at the University of California at Riverside, has developed what he calls the Affective Communication Test to measure this ability to send emotion, to be contagious. The test is a self-administered survey, with thirteen questions relating to things like whether you can keep still when you hear good dance music, how loud your laugh is, whether you touch friends when you talk to them, how good you are at sending seductive glances, whether you like to be the center of attention. The highest possible score on the test is 117 points, with the average score, according to Friedman, somewhere around 71.

What does it mean to be a high-scorer? To answer that, Friedman conducted a fascinating experiment. He picked a few dozen people who had scored very high on his test — above 90 — and a few dozen who scored very low — below 60 — and asked them all to fill out a questionnaire measuring how they felt "at this instant." He then put all of the high-scorers in separate rooms, and paired each of them with two low-scorers. They were told to sit in the room together for two minutes. They could look at each other, but not talk. Then, once the session was over, they were asked again to fill out a detailed questionnaire on how they were feeling. Friedman found that in just two minutes, without a word being spoken, the low-scorers ended up picking up the moods of the high-scorers. If the charismatic person started out depressed, and the inexpressive person started out happy, by the end of the two minutes the inexpressive person was depressed as well. But it didn't work the other way. Only the charismatic person could infect the other people in the room with his or her emotions.

Is this what Tom Gau did to me? The thing that strikes me most about my encounter with him was his voice. He had the range of an opera singer. At times, he would sound stern. (His favorite expression in that state: "Excuse me?") At times, he would drawl, lazily and easily. At other times, he would chuckle as he spoke, making his words sing with laughter. In each of those modes his face would light up accordingly, moving, easily and deftly, from one state to another. There was no ambiguity in his presentation. Everything was written on his face. I could not see my own face, of course, but my guess is that it was a close mirror of his. It is interesting, in this context, to think back on the experiment with the nodding and the headphones. There was an example of someone persuaded from the outside-in, of an external gesture affecting an internal decision. Was I nodding when Tom Gau nodded? And shaking my head when Gau shook his head? Later, I called Gau up and asked him to take Howard Friedman's charisma test. As we went through the list, question by question, he started chuckling. By question 11 — "I am terrible at pantomime, as in games like charades" — he was laughing out loud. "I'm great at that! I always win at charades!" Out of a possible 117 points, he scored 116.

In the early hours of April 19, 1775, the men of Lexington, Massachusetts, began to gather on the town common. They ranged in age from sixteen to sixty and were carrying a motley collection of muskets and swords and pistols. As the alarm spread that morning, their numbers were steadily swelled by groups of militia from the surrounding towns. Dedham sent four companies. In Lynn, men left on their own for Lexington. In towns further west that did not get the news until morning, farmers were in such haste to join the battle in Lexington that they literally left their plows in the fields. In many towns virtually the whole male population was mustered for the fight. The men had no uniforms, so they wore ordinary clothes: coats to ward off the early morning chill and large-brimmed hats.

As the colonists rushed toward Lexington, the British Regulars (as they were known) were marching in formation toward the town as well. By dawn, the advancing soldiers could see figures all around them in the hall-light, armed men running through the surrounding fields, outpacing the British in their rush to get to Lexington. As the Regulars neared the town center, they could hear drums beating in the distance. Finally the British came upon Lexington Common and the two sides met face-to-face: several hundred British soldiers confronting less than a hundred militia. In that first exchange, the British got the best of the colonists, gunning down seven militiamen in a brief flurry of gunshots on the common. But that was only the first of what would be several battles that day. When the British moved on to Concord, to systematically search for the cache of guns and ammunition they had been told was stored there, they would clash with the militia again, and this time they would be soundly defeated. This was the beginning of the American Revolution, a war that before it was over would claim many lives and consume the entire American colony. When the American colonists declared independence the following year, it would be hailed as a victory for an entire nation. But that is not the way it began. It began on a cold spring morning, with a word-of-mouth epidemic that spread from a little stable boy to all of New England, relying along the way on a small number of very special people: a few Salesmen and a man with the particular genius of both a Maven and a Connector.

In the late 1960s, a television producer named Joan Gantz Cooney set out to start an epidemic. Her target was three-, four-, and five-year-olds. Her agent of infection was television, and the "virus" she wanted to spread was literacy. The show would last an hour and run five days a week, and the hope was that if that hour was contagious enough it could serve as an educational Tipping Point: giving children from disadvantaged homes a leg up once they began elementary school, spreading prolearning values from watchers to nonwatchers, infecting children and their parents, and lingering long enough to have an impact well alter the children stopped watching the show. Cooney probably wouldn't have used these concepts or described her goals in precisely this way. But what she wanted to do, in essence, was create a learning epidemic to counter the prevailing epidemics of poverty and illiteracy. She called her idea Sesame Street.

By any measure, this was an audacious idea. Television is a great way to reach lots of people, very easily and cheaply. It entertains and dazzles. But it isn't a particularly educational medium. Gerald Lesser, a Harvard University psychologist who joined with Cooney in founding SesameStreet, says that when he was first asked to join the project, back in the late 1960s, he was skeptical. "I had always been very much into fitting how you teach to what you know about the child," he says. "You try to find the kid's strengths, so you can play to them. You try to understand the kid's weaknesses, so you can avoid them. Then you try and teach that individual kid's profile… Television has no potential, no power to do that." Good teaching is interactive. It engages the child individually. It uses all the senses. It responds to the child. But a television is just a talking box. In experiments, children who are asked to read a passage and are then tested on it will invariably score higher than children asked to watch a video of the same subject matter. Educational experts describe television as "low involvement." Television is like a strain of the common cold that can spread like lightning through a population, but only causes a few sniffles and is gone in a day.