Benjamin Franklin and John Cage would love the Bakken Museum's new "Green Energy Art Garden."

As a founding father of American science -- and the inventor of bifocals and the lightning rod -- Franklin would naturally embrace the novelty of a solar-powered rainmaking machine. And Cage, famous as the composer of "music" consisting of long stretches of silence interrupted by patches of ambient noise, would obviously approve of a big angular megaphone tricked out with dozens of little solar-powered devices that click and clatter, buzz and whir. He might even write a symphony for it.

Though best known as a museum of electricity and magnetism, the Bakken has been "a crossroads for science, art, medicine and literature" since it opened in 1975, said director David Rhees. Its new rooftop art garden, which will be up through Sept. 3, is designed to demonstrate that creativity is at the core of both art and science.

A pilot program that the Bakken hopes to expand in future years, the garden has four art projects powered by sun or wind. All are interactive devices that respond to human activity or entice viewers to touch or manipulate controls. Knocked together out of 2-by-4s, rubber tubing, electrical cable, tiny pumps and motors, the projects' apparent simplicity belies the research and planning that went into their fabrication.

The seven artists were chosen from about 20 applicants in a competition organized for the Bakken by Forecast Public Art, a St. Paul consultancy.

"The challenge we gave the artists was to illustrate how we can use renewable-energy sources to generate electricity in a sustainable and beautiful way," said Kelly Finnerty, the Bakken's deputy director.

Playfulness is as big a deal as beauty in most of the projects. Take the "Make It Rain" device by furnituremaker Peter Sowinski and theater manager Lucas Koski. A three-part contraption, it starts with a telescope fitted with perma-dark safety glass through which visitors are expected to focus on the sun. Sunlight in the telescope triggers an optical switch that turns on a solar-powered pump, shooting water onto the perforated roof of a nearby arbor through which it "rains" down onto a museum skylight.

Minneapolis landscape designer and artist Marjorie Pitz also uses sunlight in water play. Her "Solar Spitters" consist of three bathtub-sized basins filled with water and aquatic plants. There's a big, aqua moon-face sculpture floating and spitting water in each tub. The spitting is activated by solar panels that power submerged pumps. Visitors can interrupt the water flow by casting shadows on the solar-collecting panels. Because they rely on a readily available energy source, solar-powered water pumps are ideal for garden fountains and other landscaping work, said Pitz.

Japanese-born Mayumi Amada recycles American trash into a series of large-scale kaleidoscopes. Lined with angled mirrors, her stationary kaleidoscopes are illuminated by strings of tiny LED lights powered by wind and solar energy. She fashions recycled water and soda bottles into whirligigs attached to tiny thumb-sized generators that power the lights. Other bulbs draw power from solar panels. Patterns inside the kaleidoscopes are animated by clusters of bulbs and ornaments made from recycled egg cartons and other detritus.

Artists Daniel Dean and Ben Moren collaborated with architect Emily Stover to concoct a giant megaphone to amplify the "sound" of sunbeams. Of course, it's not the beams themselves that produce the cicada-like chirps and whirs that crackle over the terrace. The sunbeams simply activate solar cells that transmit energy to clattering devices attached to the outside of an angular, 5-feet-tall megaphone. Visitors eager for a headful of funny noises can peer deep into the mouth of the megaphone, or modulate the clatter by shielding the solar panels from sunlight.

The device worked perfectly in the artificial light of the artists' studios, Finnerty said. But when it was first installed on the Bakken's terrace, the blazing sunlight of a July afternoon set the sonic devices into overdrive, spinning them so fast that their clickers snapped and had to be replaced with sturdier models. Go, sun!