Reading Pulse Beats with the Sun's Rays
The pulse beats may be counted by this unusual method. On a clear day, when the sun is shining brightly, darken a room and select one window toward the sunlight, which should be prepared as follows: Draw the curtain part way down and cover the rest of the window with a heavy cardboard. Cut a small hole in the cardboard to admit a beam of light. Set a bowl of water on a table in the path of the beam so as to deflect it to the ceiling as shown by the dotted lines in the sketch.
Sun's Rays Deflected to the Ceiling
It is now a simple matter to show the pulse beats. Place the wrist against the edge of the bowl as shown, and the beam of light directed to the ceiling will record every beat of the pulse by short, abrupt movements.