John Pazmino
 NYSkies Astronomy Inc
 2003 November 22 initial
 2005 April 6 current
    On Wednesday 19 November 2003 the Science, Industry, and Business 
Library, Manhattan, hosted Satinder Puri to discuss the bridges in 
Manhattan's Central Park. He's a structural engineer with Arora and 
Associates; his talk was part of the continuing series of culture and 
science lectures at the Library.
    I noted this lecture in my November 2003 'NYC Events' and, yep, I 
did attend it. The Library is down the next block from my office, so 
it was awfully trivial to squeeze this event into my busy life.
    At first, a talk about bridges has nothing to do with astronomy, 
but it in fact does. I put the event in 'NYC Events' because we 
astronomers frequent the Park both for starviewings and for personal 
enjoyment. At the talk, I discovered an other important astronomy 
feature of the bridges, this being of global importance.
Second talk
    On Wednesday 6 April 2005 Mr Puri gave a return presentation on 
the bridges of Central Park. It was virtually the same as the talk 
from 2003 with an extra discussion about the 'Gates' exhibit of 
February 2005. During his several visits to the Gates he collected new 
photos of the bridges. Except for minor editing, my review of Puri's 
2003 show is just as good for this one in 2005. The few extra comments 
I offer, based on the present talk, are between bumpers '[ ]'. 
Central Park
    This year of 2003 is the centennial of the enabling law that 
created the Park and the opening of a multiyear suite of celebrations 
for the Park. Central Park, to keep the history here brief, was built 
in a region far north of the developed part of New York in the 
antebellum and transbellum era of the 19th century. The boundaries 
were at first set at 5th to 8th Avenues, 59th to 106th Streets; a 
couple years later, during construction, the northern frontier was 
extended to 110th Street. 
    Puri didn't mention, but it's common urban knowledge, that the 
Manhattan street grid was mapped out in 1811, long before the physical 
thorofares were laid down. The Park was staked out by geographic 
coordinates and the actual streets came much later. New York, the 
nucleus of our present cosmopolis, was then almost entirely packed 
south of Canal Street with only a couple avenues marked out to the 
northern reaches of Manhattan.  
    To explode one common wrong assumption, Central Park was NOT 
merely a fenced in parcel of native countryside, to be reserved from 
development. The whole effing place was deliberately sculpted and 
molded from human-made plans. The native terrain was shaped over to 
conform to this scheme. 
Pastoral grounds
    Central Park is the maturation of the European formal gardens, 
mixed with psalmic imagery. The intent was to have an eden for the 
City within which the visitor was transported to what heaven must have 
looked like in the mind of the 19th century: lakes, meadows, sky, 
brooks, rocks, and so on. Every original plant, stone, river was 
artificially placed just so with little kept from the natural relief. 
Even the hills, like Great Hill, were human-built accumulations. {some 
features of the natural terrain were incorporated into the human plan 
where convenient, to save excess construction.] 
    Because the Park is narrow, about 3/4 kilometer, but long, about 
four kilometers, it was a challenge to create the impression of vast 
open spaces. This task was complicated by the necessity to provide 
transverse roads linking the present Upper East Side and Upper West 
Side of Manhattan. To achieve this eden, surely one of the first 
applications of virtual reality!, the designers constructed the 
world's first multi-level public park. Various sections are separated 
on different platforms up to a dozen meters apart. 
    To join these levels and to cross the transverses, the Park was 
fitted with bridges, the first large scale use of this structure in a 
single public place. [In doing so, Central Park is still today the 
world's largest single collection of bridges on Earth! The structures 
are under continual study by urban planners from all over the world.] 
Mr Puri's interest 
    Mr Puri started his talk with a rundown of technical terms, like 
'span', 'abutment', 'pier', and illustrated them with toys on the 
lecture table. These were also included in his handout, which provided 
a map of the Park with the bridges marked on it, and some reference 
    He got into the subject from a friend who clued him to an exhibit 
at the Metropolitan Museum of Art. Friend described it as a show about 
bridges. Puri went, only to see it was really one of the centennial 
shows about Central Park. But some of the pictures did include 
bridges, and that sparked his interest as a structural engineer. 
    When he got home he tickled the web and found an online book 
titled, ahem, 'Bridges of Central Park' by Reed, McGee, and Mipaas. 
It's yours for download at ''. Altho he did 
elaborate on several of the bridges, I leave this discourse out here 
'coz it's in this book. (The site has several online books about 
Central Park and Brooklyn's Prospect Park.) [The book in a regular 
printed form is sold at the Urban Center on Madison Av and the Dairy 
within the Park.]  
    The talk was illustrated with computer slides of original design 
plans, early photographs and paintings, and his own photos taken this 
summer and fall. He stopped every so often to do some demo with his 
tabletop models.
The bridges
    Bear in mind that the Park was built in the mid 1800s with no 
additional bridges added since then. All the specimina in the Park 
today are the prime furniture, with accumulated repairs and restoring. 
Hence, a study of these bridges is a timewarp into engineering of a 
century and a half ago, all taken in by a weekend of strolls thru the 
Park. Mr Puri did such walks to take his pictures and inspect many of 
the structures. [One notable exception is Capstow bridge near 59th St 
and 5th Av. It was a wood bridge that decayed in the late 1800s and 
was replaced, still in the 19th century, by the present stone bridge.] 
    He noted that none of the bridges represent any marvels of 
engineering, they all being built according to the ordinary and 
routine methods of that time. However, there could be a latent feature 
in two of them, which would brand Central Park as the world's first 
application of an incredible pontifical technique! 
    By the way, 'pontifex' is usually associated with the Papacy, but 
it is nothing but the Latin word for 'bridge maker'. The early Church, 
taking over the lapsed Roman government, looked after the bridges in 
Rome. The Pope, by office, was the 'pontifex maximus', the greatest of 
the bridge makers. 
    All of us visiting Central Park see at least a couple bridges in 
the parts we habituate. Yet the number of bridges is immense for such 
a small real estate: forty-four! Or about thirteen per square kilometer. 
Actually, Puri pointed out, there were three more which were 
demolished in the 1930s as part of Park modifications. The one I 
previously knew of was pulled down to make room for the present zoo. 
[Peri found several more bridges, not in the 'Bridges' book, so the 
number is closer to 50.] 
Bridge structures 
    The concept of a bridge goes back to the caveman era, when it was 
desired to cross a stream by dumping loose rocks into it and walking 
across their tops. This is a rock pile bridge, not very fancy but 
workable. The stream continues its course thru gaps among the rocks; 
there is no attempt to dike up the stream. Central Park HAS a rock 
pile bridge! It is closed due to the slippery irregular 'deck'. 
    A step up, also from caveman times, is a rock slab bridge. This 
consists of purposefully placed flat plates of rock overlapping across 
a waterway. The deck is far smoother and safer to walk on. Due to the 
limit on slab size to hand and the instability of stacking them too 
high or long, this bridge is confined to short spans. Yes, there are 
four rock slab bridges in Central Park. 
    All the other bridges are 'regular' structures demonstrating some 
elevated intelligence, the sort of artifact on Mars that marks that 
planet as the abode of life. They are a mix of wood, masonry, and iron 
bridges. The most common shape is the arch, at least superficially. I 
say that because some arch bridges are really girder bridges with an 
arch-shaped facades. 
    Purists, Mr Puri explained, insist that a bridge must cross water, 
not other land, else it's just an overpass. Puri and most engineers 
aren't so fussy. At long as it's a structure to separate traffic on 
two levels so there's no interference, it's a bridge. I forget the 
count, but the Central Park bridges cross either water (brook, lake, 
&c) or land (roads and paths). 
Function of the bridges
    The Central Park bridges were designed for the traffic extant in 
the early to mid 1800s, except for railroads. No trains were ever 
allowed in the Park. The heaviest loading would be a horse-hauled 
carriage. Other traffic was foot or horseback. There were not even 
bicycles or skates back then. Motor vehicles were an unimaginable 
component of traffic, remaining so until the dawn of the 20th century. 
    For this loading, the bridges vary widely in strength from 
carrying only a footpath with plank deck and lacework railings, to 
very massive affairs with heavy parapets and deep deck. These latter 
proved adequate for light motor traffic today, but heavy vehicles like 
trucks are still banned. 
    The spans, the clear passage under the bridge between its side 
walls, abutments, or piers, range from a couple meters to something 
over twenty. The present day visitor may assume that the longer 
bridges were newly built, so much do they resemble contemporary 
highway overpasses. 
    Motor traffic took its toll on the bridges thru collision of the 
magnitude inconceivable to the pontifices. The bridges are duly 
repaired in one of two ways. The first is to use as much as practical 
prime materials, like stone from the original quarries and hand-hewed 
tooling. The other, for cost, durability, safety, is to employ modern 
materials while preserving the ka of the bridge. 
    Despite close to a century of hazard from motor traffic, none of 
the bridges was totaled by it. Except for the three removed as 
mentioned above, Central Park has every one of its prime bridges. [Not 
quite. Gapstow bridge, spanning the Pond at the southeast corner of 
the Park, was built in the 1890s. It replaces the prime all-wood 
structure that deteriorated beyond repair.]  
    The overall care of the bridges crossing or carrying motorways is 
done by the City's Department of Transportation. By arrangement with 
the Parks Department, it also looks after other bridges as needed.. 
Pastoral considerations 
    Pastoral in the religious sense of a peaceful ideal natural 
setting. Or that promoted by some strands of environmentalism. Every 
sightline in Central Park was supposed to land on some article of 
beauty and aestheticism. Altho it may seem hatstand to include an 
artificial bridge as a part of a natural setting, the pontifices rose 
to the mission to build structures not only of functionality but ones 
of supreme pleasure to behold. Today, after countless other bridges 
were constructed thruout the world, the bridges of Central Park still 
earn lavish accolade for their sheer beauty. 
    When the Park was built, there was no artificial nighttime 
illumination, only pathetic gas lamps here and there. The bridges (and 
every thing else in the Park) depended entirely on natural daylight. 
Today, with the ability to illuminate edifices by electric lighting, 
the bridges remain luminous only by nature. There is minor incidential 
illumination from nearby new roadway lighting, but nothing specific 
like floodlights. 
    Hence, the surfaces -- top, facades, underbelly -- of the bridges 
were made to fire or dance under sun and moon light. They are heavily 
textured by rough stone, geometric patterns, structural elements. The 
intent was to give the visitor 'eye candy' along with the trees, 
lawns, hills, and other eden-like features. 
    There have been concessions to safety and utility. The underpasses 
of many bridges were fitted with lighting to relieve the darkness 
that can prevail, even in bright daylight. Many bridges were made into 
corridors for modern utilities such as electric, signal, fiberoptic, 
telephone. In such cases the utility lines were buried in the deck or 
hidden along the parapet. There are a couple instances where a conduit 
was crudely nailed to the facade, where its line slashes across the 
bridge motif. 
An incredible pontifical feature? 
    In the talk and in the handouts, two bridges (I forget which) were 
described as made from reinforced concrete. Reinforced concrete is a 
staple material for modern structures, including bridges. It consists 
of a mat, cage, grill of steel rods laid out like a skeleton in the 
structure. Around them is placed regular concrete, tamped and shaken 
to grip the rods. The concrete and steel make a solid strong bond 
together and act as a single mass within the structure. 
    The rods also help join concrete elements, like beams and columns. 
They also make the structure resist against tension and torsion; 
concrete alone can withstand neither. 
    My recollection of history is that reinforced concrete came into 
use in the early 20th century. In fact, one major example of a seminal 
application was the New York underground transit system. 
    Allowing that the description of the two Central Park bridges is 
correct, than perhaps my history is mistaken. If so, all is well. 
    On the other hand, if the history is accurate, as it is related in 
engineering litterature, then Mr Puri's account, taken from the 
'Bridges' book, is astounding! It would document the use of an 
incredibly modern and sophisticated technique long before any one 
realized. Note that steel itself, for the rods, was not an engineering 
material until the 1880s, pioneered in the first New York skyscrapers. 
    In such a situation, the bridges of Central Park take on a 
fetching fascination. Perhaps they are the world's first use of 
reinforced concrete, then not to be tried again for the next half 
Astronomy of the bridges 
    Among the uglier fixtures in the Great Beyond is grotesque 
nighttime illumination of structures. Part of the reason is the lust 
to rid the landscape of the night phase of the diurnal cycle. The 
usual results are dismal to the max. 
    The collateral damage is that photons from the lamps cascade and 
fountain into the air, illuminating it to veil the night sky from 
view. This is one major example of reckless light pollution or 
luminous graffiti. 
    Light pollution advocates can do themselfs genuine good to spend 
time in Central Park and examine its bridges. They can then appreciate 
how, in the era of routine dark skies (altho there was plenty of raw 
noxious industrial air pollution!) the natural sun and moon light was 
    They can (digitally or chemically) photograph the bridges under 
various daylighting to show that, indeed, the absence of artificial 
lighting can be a massive blessing to their hometown. They can recount 
the heavy use of Central Park was a starviewing site, smack in the 
middle of the 21st century City for its paucity of obnoxious lights. 
(There ARE some!). Where is the American Urban Star Fest held each 
year? Fill in the blanks: C _ _ _ _ _ _  P _ _ _ . They can explain 
back home about the theme of Central Park, that humankind can live in 
harmony with nature, not fight against it. 
    Think about that when you muse at that overpass over the knoll 
while sunbathing in Central Park.