He then went to work on designing a new machine which would control both heat and humidity and create a stable environment in which reliable four color printing was possible. Carrier was inspired with the idea for his apparatus while waiting for a train on a foggy night. By the time the train arrived Carrier had gained a deep understanding of the relationships between temperature, humidity and the dew point. In 1902 he designed his spray driven air conditioning system which controlled both temperature and humidity using a nozzle originally designed to spray insecticide. He built his "Apparatus for Treating Air" (U.S. Pat. #808897) which was patented in 1906 and using chilled coils which not only controlled heat but could lower the humidity to as low as 55%. The device was even able to adjust the humidity level to a desired setting creating what would become the framework for the modern air conditioner. By adjusting the air movement and temperature level to the refrigeration coils he was able to determine the size and capacity of the unit to match the need of his customers. While Carrier was not the first to design a system like this his was much more stable, successful and safer that other versions and took air conditioning out of the dark ages and into the realm of science.