Pendulum of the Coast Survey

The pendulum of the Coast Survey, suspended from its tripod in the damp basement of the Stevens Institute in Hoboken on this Tuesday in 1872, exhibits a deviation from the predicted arc that cannot be attributed to the local gravitational constant. The oscillation is the sign; the terrestrial mass is the object; the rigid mathematical law governing the period is the interpretant which fails to achieve a perfect coincidence with the observed datum. This discrepancy is the irritant of doubt. To see what is in front of one’s eyes requires a long apprenticeship because the mind habitually substitutes the ideal diagram for the perceived sensation. The eye does not see the swing; it sees the expectation of the swing.

The apprenticeship consists in the systematic stripping away of the secondary qualities until the brute fact - the Firstness of the sensory impact - is isolated from the Secondness of the mechanical resistance and the Thirdness of the governing law. The observer must acknowledge that the silvered surface of the pendulum reflects the flickering gaslight not as a decorative effect, but as a series of discrete optical events that may obscure the exact moment of the transit. The error is not in the instrument, but in the premature synthesis of the data.

Inquiry begins when the surprising fact interrupts the habit of thought. The abductive hypothesis suggests that the temperature of the room has caused a microscopic elongation of the metal bar; the deductive consequence is that a cooling of the basement by five degrees should shorten the period by a calculable fraction; the inductive test is the labor of the next twelve hours of monitoring the mercury and the clock. Truth is that final opinion toward which the community of observers would gravitate if the investigation were pushed far enough. For the present, the task is to resist the desire for a smooth curve. The deviation remains. The adjustment of the screw is the only logical response to the persistence of the measurement.