Law of constant dew-point depression

In 1906 Carrier discovered that "constant dew-point depression provided practically constant relative humidity," which later became known among air conditioning engineers as the "law of constant dew-point depression". On this discovery he based the design of an automatic control system, for which he filed a patent claim on May 17, 1907. U.S. Patent 1,085,971 was issued on February 3, 1914.