NEWCASTLE, England — There is more riding the waves here than surfers, thanks to a growing number of scientists, engineers and investors. A group of entrepreneurs is harnessing the perpetual motion of the ocean and turning it into a commodity in high demand: energy. Right now, machines of various shapes and sizes are being tested off shores from the North Sea to the Pacific — one may even be coming to the East River in New York State this fall — to see how they capture waves and tides and create marine energy. The industry is still in its infancy,...