Ulbricht’s Kugelphotometer

William Manchester’s history of the ending of Middle Ages, A World Lit Only By Fire, covers the historical period of about 500 C.E. to 1521, but it could as easily refer to civilization until the end of the 18^th century. Aside from intellectual curiosities like bioluminescence and triboluminescence, humans depended upon fires, candles and simple lamps until around the turn of the nineteenth century. That century saw an accelerating and dramatic change in the way people lit their homes, their businesses and their streets. And that brought with it the need to measure that change.