Recreational thrill-seekers have been searching for adventure for centuries. The oldest ancestor of the roller coaster, for example, may have been a sled -- or maybe just a bearskin -- on a snowy hill.

In the 15th and 16th centuries, Russian villages often built wooden ice slides in the winter, sometimes 70 feet high with downhill angles of 50 degrees. Adventurers would sit on blocks of ice and let gravity have its way. In the early 1800s in western Europe, the French built similar "Russian Mountains" for use in the summer time. To do this, the French added wheels. Yet the practice never made it across the Atlantic. It wasn't until 1827, with the creation of the Mauch Chunk Switchback Railway, that America saw its first coaster. Although originally built to transport coal through the mountains of Mauch Chunk, Pa., according to Robert Cartmell's book The Incredible Scream Machine, the railroad changed its cargo exclusively to passengers in 1873 when a more efficient railway for coal was built. People paid a small fee to coast down treacherous mountain terrain. The new attraction, known as the "Switzerland of America," drew more than 35,000 customers a year. In 1976, the track's remains were declared a historic monument, and although its original purpose was not for entertainment, the railway has gone into the record books as the highest and longest coaster ever built. The total drop was 1,126 feet over 18 miles. In the early days, Europe was still the pioneer in coaster history. The idea for the first looping coaster sprung from a popular childhood toy in England and France known as the "Loop-the-Loop." It used centrifugal force to hold a ball on a track as it rolled through a loop. In 1846, Paris became home to the first "Loop-the-Loop" roller coaster, which included one small loop, 13 feet high. New York City's Coney Island, home to several amusement parks, followed with its own looping coaster in 1901. Using an ellipse rather than a circle for the loop, it advertised an excellent safety record even though there were no harnesses. It relied on the laws of physics. Because only four passengers could ride at a time, it did not make enough money to stay in business. One of the first coasters built in the United States for pleasure was Coney Island's Switchback Railway, in 1884. Modeled after the Mauch Chunk, it had a wooden frame, much slower speeds and a height less than half that of its predecessor -- about 600 feet. Workers pushed the train up to the starting point at the top of the first hill, and riders climbed stairs to board it. It rolled down and over a few small humps before stopping. There was one problem -- it couldn't make it up the next big hill. To continue the ride, passengers were required to leave the train as attendants pushed the train to the top of another drop. That rather obvious defect was remedied later that year when another coaster at Coney Island was built, this time with a track that curved back to the start and with ropes to haul the train to the top for each new ride. As with its predecessor, seats faced the side to give passengers a scenic view. Then, roller coaster popularity exploded. During the early 1900s, scenic rides gave way to exciting rides as engineers experimented with greater heights, faster speeds, more loops and more curves. State fairs and circuses were loaded with experimental tracks, some of which claimed to defy the laws of physics. A natural law, of course, can never be broken. By the 1920s, more than 1,500 coasters were operating across the country and hundreds more were to come. Coney Island drew most of the attention with its celebrated Cyclone, completed in 1927 and noted as the finest of its time. Although not very long, the Cyclone was steep -- the drops sloping down between 53 degrees and 60 degrees. The steepest modern-day coaster is 60 degrees. John Miller, co-creator of the Cyclone, prospered. Often referred to as the "Thomas Edison of roller coasters," he helped to create the modern high-speed coaster. He patented more than 100 safety devices and other coaster technology. One of his more famous inventions was the "safety ratchet," which prevents cars from rolling backward while being hauled to the top of the first drop. Before that he patented a device that held the train cars to the track. Over the next 40 years, roller coaster popularity experienced as many ups and downs as the rides. Although there were some important peaks, mostly it declined. More than 2,000 amusement parks with at least as many coasters went out of business, and only about 120 new coasters were built. The few coasters that survived the Depression had waiting lines three to five hours long. In the summer heat, those waiting in line often became argumentative, and fights resulted in several murders. The bad publicity hurt business. Over the years, several amusement parks opened and closed at Coney Island. Today the area hosts various carnival amusements and rides. Despite the overall decline, there were some bright spots. In the 1950s, Disneyland opened the Matterhorn, which introduced tubular steel tracks. These let trains travel faster and quieter. Similar tracks would later be used to build inverted and suspended coasters. In 1968, coaster designers and builders made another advance with the Thunderbolt in Pittsburgh's Kennywood Park. Cartmell's book describes the ride's new technology, design, twists, turns and scenery and adds: "The key to the Thunderbolt is a chain lift at the middle rather than the beginning of the ride. Midway throughout the Thunderbolt, after having left the chain lift, cars bruisingly whirl through turns that so jumble directions, the disoriented rider loses track of the ravine {at ground level}. Without warning, the train again drops into the valley, this time with severe plunges of 80 and 90 feet." Although the Thunderbolt was successful, coaster historians do not peg the end of coasters' dark ages until April 20, 1972, when Kings Island and its Racer coaster opened in Cincinnati. Popularity grew again, and a new phenomenon emerged -- enthusiasts who would travel from coaster to coaster over a concentrated period of days, looking for more thrills. But with thrills comes the fear of disaster. Throughout the history of the coaster, accidents, fires and miscalculations have tormented the industry. Trial-and-error was a common approach to early designs. The most dangerous of the early inventions were the Third Railers, built in the early 20th century. The track included a central third rail that supplied electricity to motorized cars. Maintenance workers were electrocuted. Motormen could drive the train as fast as they liked, accelerating through turns quick enough to send the trains off the track.

These accidents, like many in later times, were caused by careless operators or unruly passengers. Today, many coaster accidents are the result of neglected safety checks.

Traveling carnivals often are to blame. Because the rides are not permanent, the frequent dismantling and reassembling strains the hardware. Furthermore, these machines do not undergo the stringent safety checks required at permanent amusement parks -- which often include several test-runs a day before the ride is deemed ready for the public. According to the Consumer Product Safety Commission, there are almost 3,800 injuries annually involving amusement rides at permanent locations, out of a total of 290 million visits made to the parks. Of those injuries, 2 percent are serious enough to require hospitalization. Fewer than 20 percent of ride-related injuries are caused by design, operation or maintenance problems. Most injuries are the result of horseplay, patron negligence or other human error not related to the condition of the ride. The International Association of Amusement Parks and Attractions calculates that there is a 1 in 7 million chance of injury on a roller coaster and a 1 in 250 million chance of fatality. With increased safety improvements, roller coasters now are a staple at amusement parks around the world. And modern engineering technology is leading to ever more exhilarating rides. One of the newest examples was this year's opening of a coaster called Alpengeist at Busch Gardens in Williamsburg. Advertised as "the world's tallest, fastest, most twisted, hanging roller coaster," the ride includes a 17-story drop on an inverted track, and speeds reaching 67 mph. Passengers are seated in hanging cars resembling chair-lifts at ski slopes. Though a far cry from the genteel Switchback Railway of a century ago, modern coasters still rely on the same few laws of physics to deliver a few minutes of excitement. CAPTION: Coney Island's first roller coaster, built in 1884. CAPTION: The world's first loop-the-loop roller coaster was this one built in Paris in 1846.