An improved probe useful for measuring emissions of stack gases is equipped with a means for measuring moisture content and molecular weight of stack gases. A water feed tube is provided through the distal end of the probe and is fed water via a water feed line. An electrical temperature measuring device and water soaker device having spaced apart soaker feed holes is provided near the distal end of the water feed tube while a dry tubing encases the water feed tube below the temperature measuring device. A soaker wick encases part of the water feed tube and covers all of the temperature measuring device. Finally, an internal seal is provided between the dry tubing and the temperature measuring device to prevent thermally conductive heat from reaching the temperature measuring device. This structure enables the probe to make wet bulb-dry bulb measurements of stack gases.