Keeping Time On The City’s Watch

April 11, 2013 | by Sam Robinson


Scaffolding inside City Hall tower keeps access to the clocks available | Photo: Bradley Maule

Scaffolding inside City Hall tower keeps access to the clocks available | Photo: Bradley Maule

Philadelphia, 1899: Population expanding by a quarter million a decade, miles of new rail lines and terminals, electric power spreading rapidly, thousands of mills and factories; steel, coal smoke, cobble stones. The grit and tarnish of the fading Gilded Age. A self proclaimed “workshop of the world.” Towering over it all, visible for miles in all directions, brand new for a new century, was Big Penn, the 50-ton goliath, the City Hall clock.

The largest and highest in the world when it was installed, the clock’s four illuminated faces shining out over the primary bisecting streets of the City were an unsubtle declaration of the themes of an age, progress, mechanical prowess, scientific advance: a certain self-congratulatory air at having brought order to an unruly place. Travelers rushing for trains at the old Broad Street Station depended on the clock to set their pace, shopkeepers in Center City looked up to know when to close, and residents as far as thirty miles away would peer off in the direction of Philadelphia to adjust their home timepieces. The Inquirer published poems of praise; people were proud of their clock. From 362 feet above Broad and Market, the City Hall clock was the metronome setting the beat, not just for Philadelphia, but for the entire region.

Today, with every iPhone and Android updated automatically to a standardized time, and City Hall hemmed in on all sides, it is hard to conceive of an era in which an entire city took its cue from one central location. Still, as scores of wedding parties soon to be lining the median of South Broad attest, the tower and its four massive clocks remain a powerful part of the iconography of the city.

Spring forward, please don't fall back | Image: PhillyHistory.org

Spring forward, please don’t fall back | Image: PhillyHistory.org

City Hall’s original clock was constructed with a touchingly obsessive attention to detail. The installation of the clock high in the tower of what was expected to be the tallest building in the world was a problem that had vexed the Public Building Committee’s Clock Committee for years. The clock they proposed would be one of the world’s largest, and there would be not just one, but four faces which had to run together. The Committee initially rejected conventional mechanical clocks as too feeble to stand up to the gales expected to swirl around the tower. Electric clocks were likewise rejected—electric current then being too novel and uncertain to be relied on for such an important job.

After a study—what might today unkindly be called a junket—of the leading clock towers around the world, John S. Stevens, Chairman of the Clock Committee, proposed a device powered by compressed air, apparently having been impressed by a similar, albeit smaller pneumatic clock in Newark, New Jersey. After extensive testing of the principle, a contract for construction of the clock was awarded to the Johnson Temperature Regulation Company of Milwaukee, at a cost of $27,960.

The clock was designed with redundancies at every expected point of failure. Two electric engines provided constant pressure of 10 lbs. per square foot in a cylindrical tank. If either failed, the other could maintain pressure. If both motors failed, not two but three water powered motors 340 feet below in a dynamo room were kept constantly idling to pick up the slack. Even the water pressure powering these motors came from separate sources: one pipe fed water from the City’s George’s Hill Reservoir near the present Mann Center, the other from the Corinthian Avenue Reservoir a block north of Eastern State Penitentiary.

The master clock mechanism, made by the German firm Strasser & Rohde, was located at the southwest corner of the seventh floor of the tower in an air tight, temperature controlled, magnetically shielded metal case. A separate Swiss made auxiliary clock was also available in case the master failed. At noon every day but Sunday, a telegraph signal from the Naval Observatory in Washington sounded by the clock, allowing it to be manually synced to Eastern Standard Time, which in that era before atomic clocks, was determined by observation of stars crossing the meridian.

Each minute the clock mechanism, wound by hand monthly, opened a valve, allowing 700 lbs. of pressure from the compressors to travel through heavy lead piping two hundred feet up the tower to regulators in glass cases beneath each clock face. These regulators translated the air pressure to a slender metal rod extending upward some twenty feet to a set of finely calibrated gears which in turn connected to the clock hands mounted on ball-bearing axles.

A 1901 cross section shows how the 7th floor mechanism powered the clock above

A 1901 cross section shows how the 7th floor mechanism powered the clock above | Image: The Journal of the Franklin Institute, 1901

The clock faces themselves, each 26 feet in diameter, were constructed of cast iron and covered with bronze to prevent corrosion. About two feet behind each face, a white painted reflector plate holding 150 incandescent light bulbs illuminated the 3/8″ plate glass of the face at night. The minute hand of the clock was nearly eleven feet in length, the hour hand roughly nine. An informal study conducted by the Inquirer a few days after the clock was put into use found that the time could be determined from roughly a mile away in any direction by “persons with ordinarily good eyesight.”

One common feature the Clock Committee decided to omit was a bell or gong to mark the hours, for fear that the courts sitting in City Hall would prohibit its use. Apparently these courts jealously guarded their silence and had gone so far as to enjoin construction while they were in session. The deep D-note which since 1926 has been heard on the hour (or a few minutes after) in Center City, and is occasionally confused as coming from City Hall, actually issues from the Founders Bell in the old Wanamaker Men’s Store building at One South Broad (now occupied by Wells Fargo on the lower floors).

The clock was put into service at midnight on December 31, 1898. “White beams of electric light flashed north, south, east and west,” the Inquirer reported, “through the four great dials of Philadelphia’s new timekeeper, just as bells boomed and whistles whortled the midnight hour.”

The complexity of the pneumatic contraption, with its duplicative valves, tubes, and flywheels was, not surprisingly, its downfall. Within an hour of its start, the hands of the clock on the North facing side were halted by an accumulation of ice; thereafter frequent stoppages were attributed to air and water leaks, faulty wiring and blown fuses, freezing temperatures, coal smoke, and lightning strikes. Four years after the installation of the clock, the Inquirer wrote that twenty-five stoppages had been reported. Regular newspaper articles chronicling these stoppages over the next forty years suggest both the rickety nature of the design, but also the extent to which Philadelphian necks were craning towards the clock. Every time it stopped, hundreds of calls flooded City switchboards.

While the air powered system driving the hands of the clock was prone to failure, the clock mechanism itself was quite accurate, and was responsible for one of the more interesting timekeeping features of City Hall. Starting in 1906, every night at precisely 8:57, the lights of the tower, which were connected to the clock, were extinguished for three minutes, allowing residents of the region within view of the tower to adjust their home time-pieces by reference to official Philadelphia time. It is not clear when this practice was discontinued.

The same small motor boxes that have powered City Hall's clock since 1947 continue to do so today | Photo: Bradley Maule

The same small motor boxes that have powered City Hall’s clock since 1947 continue to do so today | Photo: Bradley Maule

Illustration showing scale of small electric motors powering the enormous clock | Image: The Journal of the Franklin Institute, 1901

Illustration showing scale of small electric motors powering the enormous clock | Image: The Journal of the Franklin Institute, 1901

Tending to the clock was the duty of one beleaguered man—Joseph G. Gaskill—keeper of the City Hall clock from its inauguration to 1949. Two years before the end of his term, in what must have been a bittersweet sign of the times for the old clocksman, the original sapphire gemmed master clock was finally retired. In its place, the City installed four electronic synchronous motors, each powering an individual clock.

If the elaborate pneumatic mechanism was overkill, the tiny electric motors, which continue to power the clocks to this day, are underwhelming. Each sits in the original regulator case on top of a small empty wooden cabinet, generating something on the order of a single horse worth of turning power. These clocks attach to the original drive rod and mechanisms above the case, the difference being that these clocks turn the rod constantly, imperceptibly, as opposed to in half minute increments, as with the pneumatic clock. Visitors to the observation deck can see the clock faces and mechanisms briefly as the elevator passes on its way up and down from the observation deck above.

With the installation of the new mechanisms, the accuracy of the clock improved markedly. Newspapers no longer reported regular stops. Then, in the mid 1980s the City began the long overdue reconstruction of the metal domed tower. Through nearly 72 months of construction the clocks were stopped, hidden behind some of the 150 vertical feet of scaffolding used to replace the 2,000 iron plates that make up the dome. Contractors also installed new frosted glass and halogen lighting fixtures to illuminate the faces. When the scaffolding eventually came down, and the clocks were restarted, problems surfaced immediately. Six years out of action had allowed the carefully tuned gears, which control the relationship between minute and hour hands, to rust, and ball bearings in the axles to corrode, straining the small motors driving the clocks.

The different resistance created by the corrosion apparently also caused the four clocks to run at slightly different speeds. Each of the clock motors were repaired in the mid-1990s by tower clock repair specialist Bob Rodgers of Harrisburg. Rodgers says that the most exciting aspect of the repair was being up close and seeing the hands—which move imperceptibly from street level—flying around the dial. With a circumference of over eighty feet, the minute hand must travel over a foot a minute to make its way around the dial. These repairs seem to have put things right with the clocks, and now a stroll around City Hall shows them to be in nearly perfect unity.

City Hall clock's amber glow | Photo: Bradley Maule

City Hall clock’s amber glow | Photo: Bradley Maule

One minor point of controversy concerns the “amber glow” of the clocks at night. While the lights illuminating the clock faces were originally bright incandescent white, over time the plate glass of the faces were yellowed by the same sulfurous coal smoke that stained the stone of the Hall. By the 1940s, newspapers were frequently describing them as yellow. In 1963, the City decided to make it official, and after a cleaning, tinted bulbs were installed to preserved the look, a decision which remains controversial in some quarters today, with conservation buffs periodically calling for the original white to be brought back, and others appreciating the current look. One good solution to end this Butter Battle would be to install color-changing LEDs to replace the inefficient halogens currently lighting the faces. An LED system would allow the four clock faces to match other building accent lighting in Center City to celebrate special occasions, as well as to offer a glimpse of the clocks as they originally appeared.

While the day of the public clock has come and gone, and the clocks in City Hall have been eclipsed by larger clocks elsewhere—the current largest is on the Mecca Royal Hotel Clock Tower—these clocks can continue to serve as a reminder of a time when all of Philadelphia looked to City Hall to set the time, even if that time was occasionally only right two times a day.


The author would like to thank Greta Greenberger, indefatigable champion of all things City Hall, for granting access to the tower, and for her helpful anecdotes, clock related and otherwise.


About the Author

Sam Robinson Sam Robinson is an attorney living in Philadelphia where his professional wanderings occasionally cause him to stumble across lost corners of the City landscape.


  1. J.D. says:

    Having just returned to Philly, I’ve noticed the clockfaces have become more conspicuously yellow, in my absence, and in a cartoonish, overkill way, rather than a subtle, amber ‘glow of time’ kind of way.

    I left philly in the early eighties and have since moved back, last year. One of the first things you notice isn’t the new things, it’s the old things that have been accidentally revised or re-designed in some well-intentioned update. Too bad about that color, but there’s always the hope with these things that they’ll be allowed to collect a little ash & grit and settle down to a less exaggerated, less phosphorescent kind of presence.

    Your mention of the LED possibility is something that would be disastrous. Not the cost or sustainability aspects; but the fact that they are flexible, available nightly for well-meaning color experiments and ‘displays’. The formalized, elegant lighting scheme of east coast cities– originally beautiful in their restrained white-light-on-black of the last century– has been lost. Starting in new York, the hope of restraint has been thoroughly dumpsterized for all time with the installation of crass multicolor building illumination.

    If you like your city flashing all colors of all seasons, sports teams, religious holidays, and surely, some whimiscal mashups, maybe even some real lapses in taste along the way– (you could move to vegas, but) great, let’s go for all-programmable led technology. I can foresee new radiating, pulsing patterns chasing all over, out-doing and clashing with each other, making a real circus of the once elegant city. (I would say I also see the corporate logo sneaking its inevitable way into the mix… but no, never, that couldn’t happen, right ?)

    Does anyone really think that once we have dynamic, programmable, multicolor, and presumbably animated text & logo capability lighting arrays— city hall clock or elsewhere– that cooler heads will prevail and it will be left as a subtle ambiance rather than an opportunity to sell!-inform!-interact!…. ?

    If you do, you haven’t been paying attention. Lighting has to be considered as every bit as consequential as major architecture or street sculpture– especially considering its vulnerability once controlled by unexpected hands on the controls. There are those who would love to have those clockfaces as a big, four-way jumbotron. Maybe just around the edges, at first.

  2. Harry Kyriakodis says:

    City Hall clock was sometimes called “Big Penn.” I’ve tried in vain to find out when the practice of extinguishing the tower lights for three minutes was discontinued. It seems to have been in the 1930s. By this time, mass communications (radio) permitted keeping an accurate timepiece at home and on your wrist.

  3. Harry Kyriakodis says:

    Great piece, by the way!

  4. steve m says:

    Which is more impressive: Big Ben or Big Penn ?

    1. Howie Hangg says:

      Depends on your perspective!

  5. Tom says:

    The clock use to flash at 9pm every night so you could set your watch to it anywhere on Broad street. They should get that going again.

  6. shawn says:

    I too thought it would be fun if City Hall’s clock changed colors. Though, my suggestion was to program it to change extremely slowly through the year, subtly making it through 365 colors of the rainbow. Could be timed with the seasons: cool purples and blues in the late fall/winter, greens to yellows in spring/early summer, and oranges to reds in the late summer/fall. You’d never notice it day-to-day, but once in a while look up and see a different shade and think, hey its greener than when i saw it last, summer’s almost here!

    Of course, it might be too lost amongst the LED clownpaint that exists now.

    1. Deborah Veight says:

      Just a quick question?
      Is this clock
      A Lukens Clock
      Like the one gifted to William Penn in City Hall?
      By the Lukens family (Clock makers) famous in Philadelphia Pa

  7. John G. Livewell says:

    Great writing, with great detail. Loved it.

  8. Tom Moran says:

    FANDAMNTASTIC piece, Sam. This clock reminds me of another clock that has been a
    part of my life, the Colgate clock in Jersey City. It, too, is alive and well and
    continues to “keep on ticking”. It benefits the ‘millions’ who work/live in Lower Manhattan. It’s of no informational value to residents of the Garden State, unless you’re standing in front of it.

  9. Pamela Hill says:


    My great Grandfather, George McDevitt, was the official clock watcher by night.
    I have an copy of a newspaper article detailing the work of Joseph Gaskill and my great-grandfather. Unfortunately, the article does not list the date or the newspaper who published it.
    Can you offer any assistance as I would like more information if possible.
    Thank you.

  10. Howie Hangg says:

    Growing up in Philadelphia I was told that City Hall’s clocks were referred to as “Big George”. Was I misinformed?

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