Ashby's age-of-materials plot

Tom revises his own attribution date (1992, not 1980), and notes Ashby quietly corrected the original "metallurgy is dead" framing in the fourth edition.

I showed you on the first or second day of class this Ashby plot — materials used through the ages. It turns out I was wrong about the date. I went back to his books. I thought it was from one of his 1980 books; it was actually from Material Selection and Mechanical Design, and the first time I could find that plot was 1992. He has books going back to 1980, but they don't have that plot. So here's the plot, and that's where my slide came from.