Toward the rear and on top of the boiler toward one side there is a device that looks like a package of cookies standing on edge with a broom handle sticking out of the end? There is an areal view of some 2-6-6-6's in front of the book; C&O Power that shows this device. The Virginian 2-10-10-2 also has this device and there are probabily others as well.

Anyone know what this thing is? What it does? how it works?