Reader comment: moon_custafer says:
You can use this to evoke the photography of the 1840s, when the exposure time was too long for passers-by to register! (as seen in the following photo of Nelson's Column under construction.
Mark Frauenfelder is the founder of Boing Boing and the editor-in-chief of MAKE and Cool Tools. Twitter: @frauenfelder. His new book is Maker Dad: Lunch Box Guitars, Antigravity Jars, and 22 Other Incredibly Cool Father-Daughter DIY Projects