Long, long ago in a browser version far, far forgotten, I bookmarked a picture from the Flickr photostream for the Library of Congress. At the time the picture was titled, “What’s this gadget?” The “gadget” has since been identified – the machine is visibly a lathe, but I was always intrigued by the circular, almost steampunk contraption atop the tool. More details below!
Hecox, C.W. Instructor in Machine Shop, D.C. Public Schools, supervising manufacture of practice shells for Navy at McKinley Training School, Washington, D.C.
C. W. (Clarence Wirt) Hecox (1872-1951), an instructor in the machine shop at McKinley Training School, Washington, DC, supervising a student using a lathe in the manufacture of practice shells for the U.S. Navy. The basket weave dome is a venting cover for the lathe motor (in addition to the other safety features Bill Forbes said).
– excerpted from original caption, with information added.