Henderson's idea sounds simple enough. People, cars and animals have weight. That's a physical fact. When they move around, they move the weight from one spot to another. Henderson wants to capture some of the energy created when gravity pulls on those objects as they move; the weightier the objects, the more energy there is, he says.

For cars, what he's come up with is a device he calls the "traffic tap," which is a fluid-filled sleeve that's fitted under the roadway (in prototype models, it would sit on top of the road). As a car passes over the device, the vehicle's weight forces the fluid in the sleeve through an electric generator, which produces a current. The spring-loaded sleeve then instantly refills to prepare for the next car.

"Every time a wheel passes over the device, it's generating at minimum 500 pounds of pressure," Henderson said. "We envision that the power generated could be used to power devices along the road -- like construction equipment. Or if there's enough of these and there's a lot of traffic, we could have them basically powering an entire city."

Henderson's company, Gravitational Systems, has applied for patents on the device and has received pending status, and he said that he is "in talks with" transportation officials in New York, Delaware and Virginia to determine a good way to test out the devices in the field.

Promising idea, right? Then how come energy experts -- when asked about it -- reacted as if they'd been asked to comment on some rogue science -- eugenics or alchemy or cold fusion.

"Are you serious? Is this April 1st?" asked Evan Mills, an energy scientist at the Lawrence Berkeley National Laboratory, when asked whether the traffic tap could work. "I've never heard of anything like it, and frankly it doesn't seem plausible."

Why not? Isn't this just like hydroelectric power -- getting power from something already flowing?

"No, it's completely different," Mills said. "First, the energy of falling water is immense. The energy of goop passing through a turbine is not. And then ..."

Mills thought about it for a few seconds and said, "Let's say you take all the energy that's in a car for a mile -- that's 1/27th of a gallon of gas, if the car gets 27 miles per gallon. Now, divide that by 5,280 to find out how much energy you get in a one-foot segment. That's the most energy you can get from this -- that's assuming this is 100 percent efficient. And if that's the case, why wouldn't you just burn the gas to get the electricity?"

A similar comment came from Dennis Maez, who works at the National Renewable Energy Laboratory. In an e-mail to Henderson, he wrote, "Essentially you are converting a loss in fuel efficiency into electricity. The laws of physics simply dictate that there will be losses in efficiency each time you convert from one source of power (the power used to move your car) into another (electricity generated from water pressure created from the movement of your car). The end result -- everyone paying more for gas and dirtier air."

But Henderson thinks that these criticisms are off the mark. "People don't understand how this system works," he said. "This has very little to do with the forward motion of the car, which is what is being powered by gas. It's about the weight of the car. There is inherent horsepower in the weight. Think about it this way: How much energy would it take a crane to lift a car a certain distance off the ground? That's how much energy is in the weight of each car. This represents a basic reality of physics -- if a heavy object presses down on something, it creates pressure."

In Henderson's view, then, the forward motion of the vehicle would not be impeded as it passes over the traffic tap -- the driver would barely feel it, he said, and there would be no discernible reduction in the car's fuel efficiency.

Needless to say, this is a hard nut to crack -- how do we know if this thing will work, or if there's some fundamental Newtonian caveat that precludes this apparent loophole in nature?

Henderson says that his company has done "simulations" and computerized research, and he can tell that the traffic tap -- and the other "taps" he's developing to generate power from pedestrian and animal movement -- can be a viable source of energy.

But to other scientists, it smells rotten. "It's a something-for-nothing argument; it's like perpetual motion," Berkeley's Mills said.