The two laboratory assistants in 1905 finally succeeded in getting their invention taken up by a Hungarian lamp manufacturer. By the end of the year lamps were made that were a striking success for they could be operated at an efficiency of 8 lumens per watt. They were put on the American market in 1907, the first lamp put out being the 100-watt size for 110-volt circuits. This was done by mounting several hair pin loops in series to get the requisite resistance, tungsten having a low specific resistance. The issue of the American patent was delayed owing to an interference between four different parties, each claiming to be the inventor. After prolonged hearings, one application having been found to be fraudulent, the patent was finally granted to Just and Hanaman on February 27, 1912. [Illustration: TUNGSTEN LAMP, 1907. The original 100 watt tungsten lamp was nearly three times as efficient as the carbon lamp, but its “pressed” filament was very fragile. This lamp is in the exhibit of Edison lamps in the Smithsonian Institution.] This “pressed” tungsten filament was quite fragile, but on account of its relatively high efficiency compared with other incandescent lamps, it immediately became popular. Soon after its introduction it became possible to make finer filaments so that lamps for 60, 40 and then 25 watts for 110-volt circuits were made available. Sizes up to 500 watts were also made which soon began to displace the enclosed carbon arc lamp. Lamps were also made for series circuits in sizes from 32 to 400 candlepower. These promptly displaced the carbon and Gem series lamps. The high efficiency of the tungsten filament was a great stimulus to flashlights which are now sold by the millions each year. The lighting of railroad cars, Pullmans and coaches, with tungsten lamps obtaining their current from storage batteries, soon superseded the gas light formerly used. In some cases, a dynamo, run by a belt from the car axle, kept these batteries charged. [Illustration: DRAWN TUNGSTEN WIRE LAMP, 1911. Scientists had declared it impossible to change tungsten from a brittle to ductile metal. This, however, was accomplished by Dr. Coolidge, and drawn tungsten wire made the lamp very sturdy. This lamp is in the exhibit of Edison lamps in the Smithsonian Institution.] DRAWN TUNGSTEN WIRE After several years of patient experiment, Dr. William D. Coolidge in the research laboratory of a large electrical manufacturing company at Schenectady, N. Y., invented a process for making tungsten ductile, a patent for which was obtained in December, 1913. Tungsten had heretofore been known as a very brittle metal, but by means of this process it became possible to draw it into wire. This greatly simplified the manufacture of lamps and enormously improved their strength. Such lamps were commercially introduced in 1911.