From a July 1949 National Geographic feature on Pittsburgh titled, Workshop of the Titans. The accompanying text reads:
"These city inspectors study heavy clouds billowing from a steel mill's chimneys. Smoke is viewed with special glasses and through a hole in a Ringelmann Chart. Density is graded by matching it with shades ranging from light gray to black on the card."
Here's a vision for the Point in the downtown Horne's display window:
"At Pittsburgh's Mellon Institute a researcher prepares to feed contaminated air to an assistant, Nancy Butler, in an iron lung. Plastic bags collect the air mixtures. Results are registered on an ingenious guage. Careful control of the flow protects Miss Butler from danger."