Clock
   This electric clock was made for Prof. Frederick Barnard and the University of Mississippi ca. 1859 by Edward S. Ritchie of Boston.

   The mechanism can be seen below. The top of the mercury-compensated pendulum can be seen in the middle of the glass casing. As it swings, the energy needed to keep it going is supplied by the magnetic coils on either side. Barnard described the clock in the Proceedings of the American Association for the Advancement of Science in 1859.

   The clock is on display at the University Museum of the University of Mississippi in Oxford.
   This clock pendulum apparatus is at the Physics Department at the University of Texas at Austin. 

   It is unmarked, but it is probably close to the following piece of apparatus in the 1888 catalogue of James W. Queen of Philadelphia: 

   "Pendulum Apparatus. Base and pillar of polished mahogay, with arm of brass, supporting two seconds' pendulums, one with solid brass ball, the other with a hollow one; and two other pendulumus, with solid balls, one one-forth, the other one-ninth the length of the seconds' pendulum ...$8.00"

   The meter-long pendulum that ticks once per half oscillation is often called a seconds pendulum, even though it really has a two second period. The period is proportional to the square root of the length; the shorter pendula thus have one-half and one-third the period of the longest pendulum
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