Abstract: An apparatus for measuring the dew point humidity of air, e.g. from compressed air lines of any tupe (for example, brake lines of railroad trains), composed of a conduit with a connector at one end for connecting the conduit to a source of air to be measured, a T-branch in which a probe of a dew point humidity meter is receive with the tip of the probe extending into a stream of air or other gas flowing through the conduit, and an electrical power supply for the meter, all arranged in a convenient, portable assembly.