Methods of Timekeeping in 1775
Where clock time was given, it differed from the temporal conventions we keep today. Since 1883, Boston has run on Eastern Standard Time, which was invented to synchronize railroad timetables. In 1775, watches and clocks were commonly set by sunlines at high noon, or by what is called today local apparent solar time.
All estimates in this work should be understood as an approximation of local apparent solar time, not Eastern Standard Time. To convert from local apparent solar time to Eastern Standard Time in the longitude of Boston, one must subtract 25 minutes. If Paul Revere left Charlestown at 11:00 p.m. local apparent solar time, the equivalent would be 10:35 p.m. Eastern Standard Time, or 11:35 p.m. Eastern Daylight Time.
American clock-time in many accounts referred merely to the nearest hour. Some American clocks in 1775 had no minute hand. American narratives marked the time not by hours but natural events—sunrise and sunset, or the rising of the moon. One event was recorded as happening between first light and sunrise.
British officers tended to observe clock time and often used fractions of hours and even minutes. Elijah Sanderson, the Lexington man who was captured by the British patrol later testified, “They detained us in that vicinity till a quarter past two o’clock at night. An officer, who took out his watch, informed me what the time was” (Phinney, Lexington, 31).
Neither side appears to have synchronized watches, a practice that appears to have begun among Union armies in the west during the Civil War. In other wars during the 20th century, opposing sides set their clocks differently. This was not the case at Lexington and Concord. In some instances, British estimates of times tended to be later than those of the Americans. But the difference was small and inconstant.
One test of the accuracy of temporal estimates can be made by comparing hours of sunrise and sunset with primary estimates of the chronology of events. Many eyewitnesses on both sides wrote that the Regulars arrived at Lexington Green just at sunrise. They also agreed that the battle ended when Percy’s brigade crossed Charlestown Neck at sunset. These events may be used to assess time-keeping by participants and historians. In general they confirm the accuracy of estimates by participants, and contradict the revisions that were introduced in the literature by Coburn, French, and in some cases by Tourtellot. On April 19, 1993, the hours of sunrise and sunset were as follows:
This suggests that estimates of time by British officers were in general roughly accurate when understood as local apparent solar time. Secondary accounts by Coburn and French deliberately altered these times for the march from Cambridge to Concord, to conform with their understanding of events. They all believed that Col. Smith was “slow,” and could not square that assumption with primary estimates of the rapidity of the British march. Rather than rethinking their assumption, they revised the evidence. A comparison of solar times with contemporary estimates shows that these revisions were erroneous. The student of the battle should in general trust the preponderance of primary temporal estimates, and reject those in secondary accounts by Coburn and French. These secondary works remain very valuable in other respects, but not on questions of chronology.
SOURCE: Nathaniel Low, An Astronomical Diary; Or, Almanack for the Year of Christian Era, 1775 (Boston, 1775); solar tables, 1993.