source of neon gas, there were two principal inventions that made neon lighting practicable. First were his methods for purifying the neon (or other inert gases such as argon). Claude developed techniques for purifying the inert gases within a completely sealed glass tube, which distinguished neon tube lighting from the Moore tubes; the latter had a device for replenishing the nitrogen or carbon dioxide gases within the tube. The second invention was ultimately crucial for the development of the Claude lighting business; it was a design for minimizing the degradation (by "sputtering") of the electrodes that transfer electric current from the external power supply to the glowing gases within the sign. The terms "neon light" and "neon sign" are now often applied to electrical lighting incorporating sealed glass tubes filled with argon, mercury vapor, or other gases, in addition to neon. In 1915 a U.S. patent was issued to Claude covering the design of the electrodes for neon lights; this patent became the strongest basis for the monopoly held in the U.S. by his company, Claude Neon Lights, through the early 1930s. Georges Claude and the French company he founded have long been said to have introduced neon signs to the United States by selling two to Earle C. Anthony, the owner of Packard car dealerships in San Francisco and Los Angeles (in 1923) but no conclusive evidence of this has ever been uncovered. Instead, photographs from 1923–25 reveal a neon sign in Los Angeles, but not until 1925. A photograph of Anthony's San Francisco dealership may show a neon Packard sign in 1924 but is not conclusive. However, by 1924 Claude's company (Claude Neon) had opened subsidiaries or licensed patents to affiliated companies across the US (like Electrical Products, Company on the US West Coast) and, though neon signage caught on only slowly, by the 1930s it was common across the US, eventually becoming, for a few decades, the country's dominant form of lit signage. Ocean thermal energy conversion Claude's mentor and friend was Jacques-Arsène d'Arsonval, the inventor of the "Ocean Thermal Energy Conversion" (OTEC) concept. Claude was also the first person to build prototype plants of that technology. Claude built his plant in Cuba in 1930. The system produced 22 kilowatts of electricity with a low-pressure turbine. In 1935, Claude constructed another plant, this time aboard a 10,000-ton cargo vessel moored off the coast of Brazil. Weather and