Wall, E. J. (Edward John), 1860-1928 · London, Hazell, Watson, & Viney, ld. · leaf 57
43 The Photometer or Actimometer. pinch, and it is by no means difficult to construct one at a trifling expenditure of time, trouble, and money. For this purpose procure a one -ounce purple- shouldered pill-box from any chemist, lay the lid of the box upside down on the table, take a sharp penknife… … careful that there are no ragged edges to the slits, which would cause possibly subsequent trouble. Now take a piece of ordinary sensitised paper, or even gelatino-chloride paper will do, cut it into strips three-eighths of an inch wide, insert one end through one of the slits and into the other,…
Photography
Internet Archive · Getty Research Institute · Public domain (published before 1931). Free to use for anything.
