Water Under the Bridge

By John F. Oyler
Copyright © 2017



It’s About Time
July 13, 2017



The Bridgeville Area Historical society’s final program meeting for the 2016/2017 season was an enlightening presentation by Ken Kobus with the perfectly appropriate title “It’s About Time!” His talk focused on the significant role this area played in the development of our current standard time system.

The speaker began by explaining the complications of inventing a time system. We have chosen to base our system on twenty four hour days, with one day being the time interval between successive passages of the sun over our longitude. It would appear easy to measure time this way; all one needs is a sundial.

Unfortunately, due to the ellipticity of the earth’s orbit about the sun and the inclination of its axis to the plane of that orbit, a sundial is only correct twice a year, on the vernal and autumnal equinoxes. Consequently we have defined an hour as one twenty fourth of a day measured on those special days and labelled this as mean solar time.

A second complication is the distinction between sidereal time and mean solar time. The most precise way for us to determine the actual time is to observe the passage of polar-centric stars over our longitude. This occurs consistently every twenty three hours and fifty six minutes and four seconds. The roughly four minutes difference between sidereal and mean solar time accounts for one day’s passage of the earth around its annual orbit.

Fortunately this difference is conveniently tabulated for each day of the year, making it possible for an astronomer to observe the passage of a star, determine sidereal time, and then convert it to mean solar time.

A century and a half ago Samuel Pierpont Langley financed the operation of the Allegheny Observatory doing precisely that and then selling the correct time to municipalities and railroads all over North American. The Observatory was a significant asset of the Western University of Pennsylvania (now known as the University of Pittsburgh).

This capability made it possible for each locale to know its precise local time by correcting “Allegheny Standard Time” by the difference in longitude between its meridian and that of the Observatory (one degree of longitude represents four minutes of time). Not really a problem for a traveler heading east in a horse and buggy, but a railroad passenger going from Pittsburgh to Philadelphia would have to reset his pocket watch at Greensburg, Johnstown, Altoona, etc. to be on local time.

This was satisfactory for the casual traveler, but extremely impractical for the railroads themselves, as they required a consistent time scheme to synchronize the movement of trains throughout their system. The Pennsylvania Railroad resolved this problem by establishing its own time zones. Union Station in Pittsburgh was the boundary between two zones – Philadelphia Time (forty minutes ahead of Pittsburgh) and Columbus Time (twenty minutes behind Pittsburgh). The Station itself was on Philadelphia Time, as were all the lines going East. All of the lines going West, including the Panhandle Division and consequently the Chartiers Branch, were on Columbus Time.

This was an excellent solution for the railroad but an awkward one for Pittsburgh and its two not-yet-absorbed neighbors, Allegheny City and Birmingham. Folks on the east side of a street had their clocks set an hour later than their neighbors on the west side of the same street. In 1883 the North American railroads established a system of five standard time zones, with boundaries avoiding heavily populated areas wherever possible.

This system was finally made official during World War I when legislation intending to enforce “Daylight Saving Time” was passed by Congress. This legislation, of course, required the recognition of the railroad time zones. Minor modifications, mostly associated with local preferences regarding Daylight Saving Time, have produced our current system.

Today we can always get the precise time from the National Institute of Standards and Technology. A second is defined as the time it takes a cesium-133 atom to perform 9,192,631,770 oscillations. I think dividing the time it takes the earth to rotate 360 degrees on its axis by 86,400 was precise enough for me.

Mr. Kobus is an extremely knowledgeable gentleman on a variety of subjects, each linked to an appreciation of our historical heritage. We look forward to hearing from him again on future Society programs.

The program series will take an hiatus for the rest of the Summer. The Fall schedule will be announced in the future. The next “Second Tuesday” workshop will convene at the History Center at 7:00 pm, July 11, 2017. It will focus on the history of Bridgeville High School and the 1926 Yearbook.

Water Under the Bridge

  • "Water Under the Bridge" is a column written by historian John Oyler. It appears weekly in the Bridgeville Area News, a TribTotal Media publication, as well as in a more expanded form on his blog.

The Author

  • Aside from being Bridgeville's foremost historian, Dr. John F. Oyler is also an associate professor at the Univeristy of Pittsburgh, where he teaches classes in civil engineering.

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