A group of men looking over tall rocks to determine where the plume of smoke is coming from.

Group of Men Looking Over Rocks

A group of men looking over tall rocks to determine where the plume of smoke is coming from.

"An apparatus used to determine pressures beyond those that the McLcod gauge can discern." —The Encyclopedia Britannica 1910

Radiometer

"An apparatus used to determine pressures beyond those that the McLcod gauge can discern." —The…