William Wallace invented the carbon arc lamp in the late-19th century. Wallace’s lamp functioned by passing electricity over two thick carbon wires, resulting in an overly bright light that burned out soon after contacting oxygen. The carbon arc lamp was the precursor to Edison’s electric lightbulb. Ramirez describes how a visit to Wallace’s home and a demonstration of his invention inspired Edison to create his own electric light. Edison drew heavily on Wallace’s research. Like Wallace, he employed carbon in his light. Rather than thick wires, however, he used thin carbon filaments, which increased the light the lamp emitted. In addition, Edison created an effective vacuum to prevent the filaments from reacting with oxygen. The carbon arc lamp not only draws attention to a lesser-known inventor but also contextualizes Edison’s famed invention.

The term circadian rhythm refers to biological processes that humans, animals, plants, and microbes undergo every 24 hours. These processes, which may be physical, mental, or behavioral, respond primarily to light and dark. Ramirez discusses circadian rhythm in Chapter 5, which concerns the invention of artificial light. After detailing Wallace’s carbon arc lamp and Edison’s electric light bulb, Ramirez discusses the effects of artificial light on humans.