The building is a titanic structure that goes completely dark at night and becomes a maze of black corridors that appear to stretch on into infinity. Some illumination, and a great deal of generalized din, sifts in from the nearby square through broken windows. It has received very limited maintenance in the last half-century but will probably stand as long as the Pyramids. The urinals alone look like something out of Luxor. The building's cavernous stairwells consist of profoundly worn white marble steps winding around a central shaft that is occupied by an old-fashioned wrought-iron elevator with all of the guts exposed: rails, cables, counterweights, and so on. Litter and debris have accumulated at the bottom of these pits. At the top, nocturnal birds have found their way in through open or broken windows and now tear around in the blackness like Stealth fighters, hunting for insects and making eerie keening noises - not the twitter of songbirds but the alien screech of movie pterodactyls. Gaunt cats prowl soundlessly up and down the stairs. A big microwave relay tower has been planted on the roof, and the red aircraft warning lights hang in the sky like fat planets. They shed a vague illumination back into the building, casting faint cyan shadows. Looking into the building's courtyards you may see, for a moment, a human figure silhouetted in a doorway by blue fluorescent light. A chair sits next to a dust-fogged window that has been cracked open to let in cool night air. Down in the square, people are buying and selling, young men strolling hand in hand through a shambolic market scene. In the windows of apartment buildings across the street, women sit in their colorful but demure garments holding tumblers of sweet tea.

In the midst of all this, then, you walk through a door into a vast room, and there it is: the cable station, rack after rack after rack of gleaming Alcatel and Siemens equipment, black phone handsets for the order wires, labeled Palermo and Tripoli and Cairo. Taped to a pillar is an Arabic prayer and faded photograph of the faithful circling the Ka'aba. The equipment here is of a slightly older vintage than what we saw in Japan, but only because the cables are older; when FLAG and SEA-ME-WE 3 and Africa 1 come through, Engineer Musalam will have one of the building's numerous unused rooms scrubbed out and filled with state-of-the-art gear.

A few engineers pad through the place. The setup is instantly recognizable; you can see the same thing anywhere nerds are performing the kinds of technical hacks that keep modern governments alive. The Manhattan Project, Bletchley Park, the National Security Agency, and, I would guess, Saddam Hussein's weapons labs are all built on the same plan: a big space ringed by anxious, ignorant, heavily armed men, looking outward. Inside that perimeter, a surprisingly small number of hackers wander around through untidy offices making the world run.

If you turn your back on the equipment through which the world's bits are swirling, open one of the windows, wind up, and throw a stone pretty hard, you can just about bonk that used book peddler on the head. Because this place, soon to be the most important data nexus on the planet, happens to be constructed virtually on top of the ruins of the Great Library of Alexandria.

The Lalla Rookh

When William Thomson became Lord Kelvin and entered the second phase of his life - tooling around on his yacht, the Lalla Rookh - he appeared to lose interest in telegraphy and got sidetracked into topics that, on first reading, seem unrelated to his earlier interests - disappointingly mundane. One of these was depth sounding, and the other was the nautical compass.

At the time, depths were sounded by heaving a lead-weighted rope over the side of the ship and letting it pay out until it hit bottom. So far, so easy, but hauling thousands of meters of soggy rope, plus a lead weight, back onto the ship required the efforts of several sailors and took a long time. The US Navy ameliorated the problem by rigging it so that the weight could be detached and simply discarded on the bottom, but this only replaced one problem with another one in that a separate weight had to be carried for each sounding. Either way, the job was a mess and could be done only rarely. This probably explains why ships were constantly running aground in those days, leading to a relentless, ongoing massacre of crew and passengers compared to which today's problem of bombs and airliners is like a Sunday stroll through Disney World.

In keeping with his general practice of using subtlety where moronic brute force had failed, Kelvin replaced the soggy rope with a piano wire, which in turn enabled him to replace the heavy weight with a much smaller one. This idea might seem obvious to us now, but it was apparently quite the brainstorm. The tension in the wire was so light that a single sailor could reel it in by turning a spoked wooden wheel.

The first time Kelvin tried this, the wheel began to groan after a while and finally imploded. Dental hygienists, or people who floss the way they do (using extravagantly long pieces of floss and wrapping the used part around a fingertip) will already know why. The first turn of floss exerts only light pressure on the finger, but the second turn doubles it, and so on, until, as you are coming to the end of the process, your fingertip has turned a gangrenous purple. In the same way, the tension on Kelvin's piano wire, though small enough to be managed by one man, became enormous after a few hundred turns. No reasonable wheel could endure such stress.

Chagrined and embarrassed, Kelvin invented a stress-relief mechanism. On one side of it the wire was tight, on the other side it was slack and could be taken up by the wheel without compressing the hub. Once this was out of the way, the challenge became how to translate the length of piano wire that had been paid out into an accurate depth reading. One could never assume that the wire ran straight down to the bottom. Usually the vessel was moving, so the lead weight would trail behind it. Furthermore, a line stretched between two points in this way forms a curve known to mathematicians as a catenary, and of course the curve is longer than a straight line between the same two points. Kelvin had to figure out what sorts of catenary curves his piano wire would assume under various conditions of vessel speed and ocean depth - an essentially tedious problem that seems well beneath the abilities of the father of thermodynamics.

In any case, he figured it out and patented everything. Once again he made a ton of money. At the same time, he revolutionized the field of bathymetry and probably saved a large number of lives by making it easier for mariners to take frequent depth soundings. At the same time, he invented a vastly improved form of ship's compass which was as big an improvement over the older models as his depth-sounding equipment was over the soggy rope. Attentive readers will not be surprised to learn that he patented this device and made a ton of money from it.

Kelvin had revolutionized the art of finding one's way on the ocean, both in the vertical (depth) dimension and in the horizontal (compass) dimensions. He had made several fortunes in the process and spent a great deal of his intellectual gifts on pursuits that, I thought at first, could hardly have been less relevant to his earlier work on undersea cables. But that was my problem, not his. I didn't figure out what he was up to until very close to the ragged end of my hacker tourism binge

Slack

The first time a cable-savvy person uses the word slack in your presence, you'll be tempted to assume he is using it in the loose, figurative way - as a layperson uses it. After the eightieth or ninetieth time, and after the cable guy has spent a while talking about the seemingly paradoxical notion of slack control and extolling the sophistication of his ship's slack control systems and his computer's slack numerical-simulation software, you begin to understand that slack plays as pivotal a role in a cable lay as, say, thrust does in a moon mission.