Math student Carl Størmer acquired a hidden camera in 1890, and put it to use on the streets of Oslo.
The results are close to 500 secret images that show a wide range of people in a casual, relaxed state. Working like a paparazzo, Størmer would greet his subjects and then snap away as they approached. Friendly salutations and suspicious glances play out across his work, serving as some of the first examples of street photography.