[Note that this article is a transcript of the video embedded above.] For as straightforward as they are, there’s a lot of mystery to sewers. They’re mostly out of sight, out of mind, and ideally out of smell too. But there’s one familiar place you can get a hint of what’s happening below your feet, and that’s the manhole. Sanitary engineers know that there’s actually a lot of complexity in this humble hallmark of our least-glorified type of infrastructure. So, I set up a see through sewer system so you can see what’s happening inside. I’m Grady, and this is Practical Engineering. There are a lot of kinds of manholes. If it’s a utility of any kind and you put it underground, there’s a good chance you’ll need some access to it at some point in time. But I figure if you picture a manhole in your head, it probably leads to a sewer system: either a sanitary sewer that connects to your drains and toilets, a storm sewer that connects to storm drains, or a combined system that carries it all. Unlike what you see in movies, most sewer systems aren’t huge tunnels full of totally tubular turtles and their giant rodent mentor. They’re mostly just simple pipes sized according to the amount of flow expected during peak periods. Sewer networks have a tributary structure. Gravity carries waste along downward sloping pipes that converge and concentrate into larger and larger lines, like a big underground river system…but grosser. Terminology varies place to place, but in general, it goes like this. Pipes that service individual buildings are usually called laterals, and those servicing particular streets are branches. Larger pipes that collect wastewater from multiple branches are called mains or trunk sewers. And the most significant lines furthest downstream in the system are usually called interceptors. And connecting each one is a manhole. This is my model sewer system. I’m just pumping water into an upper manhole and letting it flow through the system by gravity. I chose to do this with nice blue water for anyone watching while having lunch. In real life, the color in a sewer isn’t quite this nice. Unlike regular plumbing, where you use “fittings” to connect lengths of pipes together, sewers lines are connected with manholes. Any change in size, direction, alignment, or elevation is a place where debris can get caught or turbulence can affect the flow. So instead of elbows or tees in the pipe, we just put a manhole instead. In fact, unlike many underground utilities, you can usually trace the paths of a sewer network pretty easily, because it’s all straight lines between manholes. They provide a controlled environment where the flow can change direction, and more importantly, a place where technicians can get inside to inspect the lines, remove clogs, or perform maintenance (hence the name). Unlike fresh water distribution systems that can usually go a long time without any intervention, sewers are a little… more hands-on (just make sure you wash your hands afterwards). There’s just no end to the type of things that can find their way into the pipes. Fibrous objects are particularly prone to causing clogs, which is why so many sewer utilities have campaigns encouraging people not to flush wipes, even if they say “flushable” on the package. Fats, oil, and grease (or FOG, in the industry) are also a major problem because they can congeal and harden into blockages sometimes not-so-lovingly known as “fatbergs”. Of course, a lot of people aren’t aware of what’s safe to flush or wash down the drain, and even for people who know, it’s easy to let something slide when it’s not your problem anymore. And in most cases, the rules aren’t very strictly enforced outside of large commercial and industrial users of the system. But if you use a sewage system, in a way, obstructions really ARE your problem because a portion of your taxes or fees that pay for the sewer system go toward sending people - not always men (despite the name) - into manholes to keep things flowing. And the more often things clog up, the higher the rates that everyone pays to cover the cost of maintenance. There’s quite a lot of sophistication in keeping sewers in service these days. It’s not unusual for a city or sewer district to regularly send cameras through the lines for inspection. Technology has made it a lot easier to be proactive. In fact, there’s a whole field of engineering called infrastructure asset management that just focuses on keeping track of physical assets like sewer lines, monitoring their condition, and planning ahead for repairs, maintenance, and replacement over the long term. A lot of the unclogging and cleaning these days is done by hydro jetting: basically a pressure washer scaled up. Rotating nozzles blast away debris and propel the hose down the line. In fact, one of the benefits of manholes is that, if a sewer line does need maintenance, it can be easily taken out of service. You can just run a bypass pump from one manhole to another and keep the system running. But maintenance isn’t the only thing a manhole helps with. You can see a few more things in this demo. For one, manholes provide ventilation. Along with the solids and liquids you expect, gases can end up flowing through sewer pipes too. You can see the bubbles moving through the system. Air bubbles can restrict the flow of fluid in a pipe, and air pressure can cause wacky problems like backflow. Along with regular air, toxic, corrosive, or even explosive gases can also build up in a sewer if there’s no source of fresh air, so ventilation from manholes is an important aspect of the system. Sometimes you’ll even notice condensed water vapor flowing up from a manhole cover. In a few cities, like New York, that might be related to an actual steam distribution system running underground. But it can also happen in sewers when the wastewater from sources like showers and dishwashers is warmer than the outside air, especially in the winter. I added a third manhole to my model so you can see how a junction might look. It just provides a nice way to confluence two streams into one pipe, which is an important job in a sewer system, since a “sewershed” all has to flow to one place. The manhole acts kind of like a buffer, smoothing out flows through the system. At normal flows, that’s not a super important job. It’s basically just a connection between two pipes. But the peak flows for most sewers, even if they’re not storm sewers, happen during storms. Drains may be improperly connected to sanitary sewers, plus surface water often finds a way in through manhole covers and other means. In fact, a lot of places require sealed and bolted covers if the top of the manhole is below the floodplain. That’s why you sometimes see these air vents sticking up out of the ground. Many older cities use combined systems where stormwater runs in the same pipes. So rainwater in sewers can be a major challenge. And you can see when you get a big surge of water, the manhole can store some of it, smoothing out the flow downstream. These storm flows are actually a pretty big problem of the constructed environment. You may have heard about the trouble with holding swimming events in the Seine River in Paris during the 2024 summer olympics. Same problem. Wastewater treatment plants can only handle so much flow, so many places have to divert wastewater during storms, often just discharging raw, if somewhat diluted, sewage directly into rivers or streams. In fact some of the most impressive feats of engineering in progress right now are ways to store excess wastewater during storms so it can be processed through a treatment plant at a more manageable rate. But overflows can also happen way upstream of a treatment plant if the pipes are too small. Sometimes that storage available through manholes isn’t enough. I can plug up the pipe in my demo to simulate this. If the sewer lines themselves can’t handle the flow, you can get wastewater flowing backwards in pipes, and if things get bad enough, you can get releases out of top of manholes. And of course, this doesn’t have to be the result of a storm. Even a blockage or clog in the line can cause wastewater to back up like this. Obviously, having raw sewage spilling to the surface is not optimal, and many cities in the US pay millions of dollars in fines and settlements to the EPA for the contamination caused by backups. Another thing this model shows is that not all pipes have to come in at the bottom. They call this a drop manhole when one of the inlets is a lot higher than the outlet. The slope of a sewer line is pretty important. I’ve covered that topic in another video. There’s a minimum slope to get good flow, but you don’t want too much slope either. Wastewater often carries rocks and grit, so if it gets going too quickly, it can wear away or otherwise damage the pipes. So if you’re running a line along a steep slope, sometimes it’s a better design to let some of that fall happen in a manhole, rather than along the pipe. It’s not normally done this way where my pipe just juts in. You usually don’t want a lot of splashing and turbulence in a manhole, again to avoid damage, but also to avoid smells. So most drop manholes use pipes or other structures to gently transition inlet flow down to the bottom. I hope it’s clear how useful manholes are by now. Doing it this way - by making the plumbing junctions into access points - just provides a lot of flexibility, while also kind of standardizing the system so anyone involved, whether its a contractor building one or a crew doing maintenance, kind of knows what to expect. In fact, if you live in a big city, there’s a good chance that the sewer authority has standardized drawings and details for manholes so they don’t have to be reinvented for each new project. In many cases, they’re just precast concrete cylinders placed into the bottom of an excavation. Those cylinders sit on temporary risers, and then concrete is used to place the bottom, often with rounded channels to smooth the transition into and out of the manhole. I did a video series on the construction of a sewage lift station and showed how a few of these are built if you want to check that out after this and learn more. Constructing manholes reminds of that famous interview riddle about why manhole covers are round. There’s a lot of good answers: a round object can’t fall down into the hole, it can be replaced in any orientation, it’s easy to roll so workers don’t have to lift the entire weight to move it out of the way. A professor of mine had an answer that I don’t think I’ve heard before. Manhole covers are round because manholes are round. It’s almost like asking why pringles lids are round. And manholes are round for a lot of good reasons: it’s the best shape for resisting horizontal soil loads. It’s easier to manufacture a round shape than a rectangular one. For those reasons, manholes are usually made of pipes, and pipes are round because it’s the most efficient hydraulic section. It’s one of those questions, like the airplane on a treadmill, that can spawn unending online debate. But I like pipes, so that’s my favorite answer.

It was 8 May 1945, Victory in Europe Day. With the German military’s unconditional surrender, the European part of World War II came to an end. Alan Turing and his assistant Donald Bayley celebrated victory in their quiet English way, by taking a long walk together. They had been working side by side for more than a year in a secret electronics laboratory, deep in the English countryside. Bayley, a young electrical engineer, knew little about his boss’s other life as a code breaker, only that Turing would set off on his bicycle every now and then to another secret establishment about 10 miles away along rural lanes, Bletchley Park. As Bayley and the rest of the world would later learn, Bletchley Park was the headquarters of a vast, unprecedented code-breaking operation. Donald Bayley (1921-2020) graduated with a degree in electrical engineering, and was commissioned into the Royal Electrical and Mechanical Engineers. There, he was selected to work with Alan Turing on the Delilah project. In later life he designed the teletypewriter-based “Piccolo” systemfor secret diplomatic radio communications, adopted by the British Foreign and Commonwealth Office and used worldwide for decades.Bonhams “That was the end of that conversation,” Bayley recalled 67 years later. Turing’s incredible code-breaking work is now no longer secret. What’s more, he is renowned both as a founding father of computer science and as a pioneering figure in artificial intelligence. He is not so well-known, however, for his work in electrical engineering. This may be about to change. In November 2023, a large cache of his wartime papers—nicknamed the “Bayley papers”—was auctioned in London for almost half a million U.S. dollars. The previously unknown cache contains many sheets in Turing’s own handwriting, telling of his top-secret “Delilah” engineering project from 1943 to 1945. Delilah was Turing’s portable voice-encryption system, named after the biblical deceiver of men. There is also material written by Bayley, often in the form of notes he took while Turing was speaking. It is thanks to Bayley that the papers survived: He kept them until he died in 2020, 66 years after Turing passed away. When the British Government learned about the sale of these papers at auction, it acted swiftly to put a ban on their export, declaring them to be “an important part of our national story,” and saying “It is right that a UK buyer has the opportunity to purchase these papers.” I was lucky enough to get access to the collection prior to the November sale, when the auction house asked for my assistance in identifying some of the technical material. The Bayley papers shine new light on Turing the engineer. Alan Turing’s Delilah Project During the war, Turing realized that cryptology’s new frontier was going to be the encryption of speech. The existing wartime cipher machines—such as the Japanese “ Purple” machine, the British Typex, and the Germans’ famous Enigma and teletypewriter-based SZ42—were all for encrypting typewritten text. Text, though, is scarcely the most convenient way for commanders to communicate, and secure voice communication was on the military wish list. SIGSALY speech-encryption system was constructed in New York City, under a U.S. Army contract, during 1942 and 1943. It was gigantic, weighing over 50 thousand kilograms and filling a room. Turing was familiar with SIGSALY and wanted to miniaturize speech encryption. The result, Delilah, consisted of three small units, each roughly the size of a shoebox. Weighing just 39 kg, including its power pack, Delilah would be at home in a truck, a trench, or a large backpack. Bell Labs’ top secret installation of the SIGSALY voice-encryption system was a room-size machine that weighed over 50,000 kilograms. NSA In 1943, Turing set up bench space in a Nissen hut and worked on Delilah in secret. The hut was at Hanslope Park, a military-run establishment in the middle of nowhere, England. Today, Hanslope Park is still an ultrasecret intelligence site known as His Majesty’s Government Communications Centre. In the Turing tradition, HMGCC engineers supply today’s British intelligence agents with specialized hardware and software. Turing seems to have enjoyed the two years he spent at Hanslope Park working on Delilah. He made an old cottage his home and took meals in the Army mess. The commanding officer recalled that he “soon settled down and became one of us.” In 1944, Turing acquired his young assistant, Bayley, who had recently graduated from the University of Birmingham with a bachelor’s degree in electrical engineering. The two became good friends, working together on Delilah until the autumn of 1945. Bayley called Turing simply “Prof,” as everyone did in the Bletchley-Hanslope orbit. “I admired the originality of his mind,” Bayley told me when I interviewed him in the 1990s. “He taught me a great deal, for which I have always been grateful.” In return, Bayley taught Turing bench skills. When he first arrived at Hanslope Park, Bayley found Turing wiring together circuits that resembled a “spider’s nest,” he said. He took Turing firmly by the hand and dragged him through breadboarding bootcamp. Alan Turing and his assistant Donald Bayley created this working prototype of their voice-encryption system, called Delilah.The National Archives, London A year later, as the European war ground to a close, Turing and Bayley got a prototype system up and running. This “did all that could be expected of it,” Bayley said. He described the Delilah system as “one of the first to be based on rigorous cryptographic principles.” How Turing’s Voice-Encryption System Worked Turing drew inspiration for the voice-encryption system from existing cipher machines for text. Teletypewriter-based cipher machines such as the Germans’ sophisticated SZ42—broken by Turing and his colleagues at Bletchley Park—worked differently from the better known Enigma machine. Enigma was usually used for messages transmitted over radio in Morse code. It encrypted the letters A through Z by lighting up corresponding letters on a panel, called the lampboard, whose electrical connections with the keyboard were continually changing. The SZ42, by contrast, was attached to a regular teletypewriter that used a 5-bit telegraph code and could handle not just letters, but also numbers and a range of punctuation. Morse code was not involved. (This 5-bit telegraph code was a forerunner of ASCII and Unicode and is still used by some ham radio operators.) The Delilah voice-encryption machine contained a key unit that generated the pseudorandom numbers used to obscure messages. This blueprint of the key unit features 8 multivibrators (labeled “v1,” “v2,” and so forth).The National Archives, London Inside the SZ42, the key was produced by a key generator, consisting of a system of 12 wheels. As the wheels turned, they churned out a continual stream of seemingly random characters. The wheels in the receiver’s machine were synchronized with the sender’s, and so produced the same characters—Y/RABV8WOUJL/H9VF3JX/D5Z in our example. The receiving machine subtracted the key from the incoming ciphertext PNTDOOLLHANC9OAND9NK9CK5, revealing the plaintext ANGREIFEN9UM9NUL9NUL9UHR (a space was always typed as “9”). now declassified report, Turing and Bayley commented that the problem of synchronizing the two key generators had presented them with “formidable difficulties.” But they overcame these and other problems, and eventually demonstrated Delilah using a recording of a speech given by Winston Churchill, successfully encrypting, transmitting, and decrypting it. This loose-leaf sheet shows a circuit used by Turing in an experiment to measure the cut-off voltage at a triode tube, most likely in connection with the avalanche-effect basic to a multivibrator. Multivibrators were an essential component of Delilah’s key-generation module. Bonhams The encryption-decryption process began with discretizing the audio signal, which today we’d call analog-to-digital conversion. This produced a sequence of individual numbers, each corresponding to the signal’s voltage at a particular point in time. Then numbers from Delilah’s key were added to these numbers. During the addition, any digits that needed to be carried over to the next column were left out of the calculation—called “noncarrying” addition, this helped scramble the message. The resulting sequence of numbers was the encrypted form of the speech signal. This was transmitted automatically to a second Delilah at the receiving end. The receiving Delilah subtracted the key from the incoming transmission, and then converted the resulting numbers to voltages to reproduce the original speech. But the war was winding down, and the military was not attracted to the system. Work on the Delilah project stopped not long after the war ended, when Turing was hired by the British National Physical Laboratory to design and develop an electronic computer. Delilah “had little potential for further development,” Bayley said and “was soon forgotten.” Yet it offered a very high level of security, and was the first successful demonstration of a compact portable device for voice encryption. Turing’s Lab Notebook The two years Turing spent on Delilah produced the Bayley papers. The papers comprise a laboratory notebook, a considerable quantity of loose sheets (some organized into bundles), and—the jewel of the collection—a looseleaf ring binder bulging with pages. multivibrator, which is a circuit that can be triggered to produce a single voltage pulse or a chain of pulses. In the experiment, the pulse was fed into an oscilloscope and its shape examined. Multivibrators were crucial components of Turing’s all-important key generator, and the next page of the notebook, labeled “Measurement of ‘Heaviside function,’ ” shows the voltages measured in part of the same multivibrator circuit. A key item in the Bayley papers is this lab notebook, whose first 24 pages are in Turing’s handwriting. These detail Turing’s work on the Delilah project prior to Bayley’s arrival in March 1944.Bonhams Today, there is intense interest in the use of multivibrators in cryptography. Turing’s key generator, the most original part of Delilah, contained eight multivibrator circuits, along with the five-wheel assembly mentioned previously. In effect the multivibrators were eight more very complicated “wheels,” and there was additional circuitry for enhancing the random appearance of the numbers the multivibrators produced. The Bandwidth Theorem Two loose pages, in Turing’s handwriting, explain the so-called bandwidth theorem, now known as the Nyquist-Shannon sampling theorem. This was likely written out for Bayley’s benefit. Bonhams sampling theorem. Turing’s proof of the theorem is scrawled over two sheets. Most probably he wrote the proof out for Bayley’s benefit. The theorem—which expresses what the sampling rate needs to be if sound waves are to be reproduced accurately—governed Delilah’s conversion of sound waves into numbers, done by sampling vocal frequencies several thousand times a second. Bell Labs, Claude Shannon had written a paper sketching previous work on the theorem and then proving his own formulation of it. Shannon wrote the paper in 1940, although it was not published until 1949. Turing worked at Bell Labs for a time in 1943, in connection with SIGSALY, before returning to England and embarking on Delilah. It seems likely that he and Shannon would have discussed sampling rates. Turing’s “Red Form” Notes During the war, Hanslope Park housed a large radio-monitoring section. Shifts of operators continuously searched the airwaves for enemy messages. Enigma transmissions, in Morse code, were identified by their stereotypical military format, while the distinctive warble of the SZ42’s radioteletype signals was instantly recognizable. After latching onto a transmission, an operator filled out an Army-issue form (preprinted in bright red ink). The frequency, the time of interception, and the letters of ciphertext were noted down. This “red form” was then rushed to the code breakers at Bletchley Park. Writing paper was in short supply in wartime Britain, and Turing used the blank reverse sides of these “red form” sheets, designed for radio operators to note down information about intercepted signals.Bonhams Writing paper was in short supply in wartime Britain. Turing evidently helped himself to large handfuls of red forms, scrawling out screeds of notes about Delilah on the blank reverse sides. In one bundle of red forms, numbered by Turing at the corners, he considered a resistance-capacitance network into which a “pulse of area A at time 0” is input. He calculated the charge as the pulse passes through the network, and then calculated the “output volts with pulse of that area.” The following sheets are covered with integral equations involving time, resistance, and charge. Then a scribbled diagram appears, in which a wavelike pulse is analyzed into discrete “steps”—a prelude to several pages of Fourier-type analysis. Turing appended a proof of what he termed the “Fourier theorem,” evidence that these pages may have been a tutorial for Bayley. Turing’s Lectures for Electrical Engineers The cover of the looseleaf ring binder is embossed in gilt letters “Queen Mary’s School, Walsall,” where Bayley had once been a pupil. It is crammed with handwritten notes taken by Bayley during a series of evening lectures that Turing gave at Hanslope Park. The size of Turing’s audience is unknown, but there were numerous young engineers like Bayley at Hanslope. Turing’s Lectures on Advanced Mathematics for Electrical Engineers. Running to 180 pages, they are the most extensive noncryptographic work by Turing currently known, vying in length with his 1940 write-up about Enigma and the Bombe, affectionately known at Bletchley Park as “Prof’s Book.” Scientific American ran an article by the legendary computer scientist and AI pioneer John McCarthy, in which he stated that Turing’s work did not play “any direct role in the labors of the men who made the computer a reality.” It was a common view at the time. A binder filled with Bayley’s notes of Turing’s lectures is the jewel of the recently sold document collection.Bonhams As we now know, though, after the war Turing himself designed an electronic computer, called the Automatic Computing Engine, or ACE. What’s more, he designed the programming system for the Manchester University “Baby” computer, as well as the hardware for its punched-tape input/output. Baby came to life in mid-1948. Although small, it was the first truly stored-program electronic computer. Two years later, the prototype of Turing’s ACE ran its first program. The prototype was later commercialized as the English Electric DEUCE (Digital Electronic Universal Computing Engine). Dozens of DEUCEs were purchased—big sales in those days—and so Turing’s computer became a major workhorse during the first decades of the Digital Age. Turing’s lecture notes are in effect a textbook, terse and selective, on advanced math for circuit engineers, although now very out-of-date, of course. Turing’s knowledge of practical electronics was probably inferior to his assistant’s, initially anyway, since Bayley had studied the subject at university and then was involved with radar before his transfer to Hanslope Park. When it came to the mathematical side of things, however, the situation was very different. The Bayley papers demonstrate the maturity of Turing’s knowledge of the mathematics of electrical circuit design—knowledge that was essential to the success of the Delilah project. report for the Bonhams auction house.

Designing research studies to determine what is going on inside the minds of animals is extremely challenging. The literature is littered with past studies that failed to properly control for all variables and thereby overinterpreted the results. The challenge is that we cannot read the minds of animals, and they cannot communicate directly to us […] The post Do Apes Have a Theory of Mind first appeared on NeuroLogica Blog.

According to this article at politico, there was an all-hands meeting at NSF today (at least for the engineering directorate) where they were told that there will be staff layoffs of 25-50% over the next two months. This is an absolute catastrophe if it is accurately reported and comes to pass.  NSF is already understaffed.  This goes far beyond anything involving DEI, and is essentially a declaration that the US is planning to abrogate the federal role in supporting science and engineering research.   Moreover, I strongly suspect that if this conversation is being had at NSF, it is likely being had at DOE and NIH. I don't even know how to react to this, beyond encouraging my fellow US citizens to call their representatives and senators and make it clear that this would be an unmitigated disaster.

As part of my job running Terraform Industries, I get to build an amazing team of super smart people, and that involves interviewing hundreds of people. Over time certain patterns have become obvious, but I remember when they weren’t obvious to me on the other side of the table! It has become clear to me that there are some subjects that should be covered as part of any professional degree and are not only not taught and not discussed, but most otherwise highly qualified graduates are completely unaware of their existence.  I have previously written about improving resumes, becoming a …