This Month in History: The humidostat debuts
The front cover of a Johnson catalog describing the new "humidostat".
Jan. 13, 1901: Warren Johnson's "20th century invention" - the "humidostat"
A Milwaukee Sentinel article from Jan. 13, 1901 announced a "twentieth century invention" created by Johnson Controls' founder Warren Johnson. The invention referred to was the "humidostat," a device that measured the moisture content of indoor air in order to increase or decrease it - much as a thermostat controls indoor air temperature.
"Prof. Johnson has invented a device to furnish moisture to the air of rooms. Has an attachment by which air is perfumed at will ... and may be changed to give prismatic scale of odor ...."
The Milwaukee Sentinel article described, in the somewhat flowery style of the day, the new product in this way: "The seemingly fanciful ideas of the Arabian Nights are becoming reality in this 20th century. Prof. Johnson has invented a device to furnish moisture to the air of rooms. Has an attachment by which air is perfumed at will ... and may be changed to give prismatic scale of odor ...."
Johnson, in his patent application, offered this description: "This invention pertains to a device for measuring or ascertaining the percentage of moisture in the surrounding air or medium, and ... according to variations in such percentage, a device for supplying or adding moisture to the air ...."
He went on to note the device is primarily designed for use in or as a part of a complete system that includes a humidifier, as well as heating and temperature-regulating apparatus.