 During the first decade of the 20th century, President William McKinley was assassinated and Vice President Theodore Roosevelt became president. Wilbur and Orville Wright invented, built, and flew the first powered aircraft at Kittyhock, North Carolina, and construction of the Panama Canal began. Around this time, it became apparent to most of the medical and scientific community that x-ray exposures, if too frequent or intensive, could produce skin burns. By 1903, Thomas Edison stopped doing x-ray research after his assistant, Clarence Dally, developed cancer and died. Ten years after the discovery of x-rays, malpractice lawsuits brought about efforts to protect medical patients from too much radiation exposure. There were people who began to advocate for practices to protect patients and healthcare workers, which included enclosed x-ray tubes and garments that shielded against radiation. It was at this time that Albert Einstein received his PhD, published groundbreaking papers that explained the photoelectric effect, formulated the theory of special relativity, and proposed the law of mass energy conservation, often seen written scientifically as E equals MC squared. The same year, the Model T automobile was introduced, and the American Renton Race Society announced that there was no excuse whatsoever for anyone being injured during medical procedures that use x-rays. During this decade, the famous Geiger Marsden experiments discovered that atoms have a nuclear nature. Scientists, Hans Geiger and Ernest Marsden, working under the direction of New Zealand physicist Ernest Rutherford, deduced that every atom has a nucleus where most of its positive charge and mass are located.