Tag Archives: history

Telluric Currents and the Earth Battery

(So it turns out I can pack boxes faster than expected!  Unfortunately that means I’m now just killing time until tomorrow when I load everything into the truck and head off for my new job in Waterloo, Iowa.  But here’s another article, just for you!  I know, I know, it’s not a project or a circuit, but I left my electronics stuff in St. Louis…)

You know what?  The Discovery Channel is right, the world is just awesome.

The other day I was surfing Wikipedia and happened across an article on telluric currents.  Apparently, changes in our planet’s magnetic field induce fairly substantial currents into the surface of the earth (both across lands and oceans).  Now, I’ve heard of the earth’s magnetic field, and I’m familiar with grounding rods acting as current paths.  But telluric currents?  Well, like 99.9% of all Wikipedia articles, it’s new to me.

Global Map of Telluric Currents, Created 1936 - This is likely no longer very accurate by today's standards.  Understandably, collecting such data wasn't so easy in 1936, so a lot of this map came from interpolation.

So what’s the deal with these mysterious earth currents?  Well believe it or not, this is a phenomenon which was first observed way back in the mid-1800s.  In fact, it used to wreak havoc with telegraph and, later, telephone lines.  You see, electrical currents tend to follow the path of least resistance.  So if there happens to be a wire connected between two points on the earth’s surface (e.g. a communications ground line), any current that might normally have flowed through the earth itself will instead flow along the lower-resistance wire.  For example, according to The Earth’s Electrical Environment (Pg. 244), between August 28th and september 2nd, 1859, an enormous geomagnetic storm induced 800V on a 600km wire in France.  Much later, on March 24, 1940, a similar event damaged two communications sites in Tromso, Norway:

“Sparks and permanent arcs were formed in the coupling racks and watch had to be kept during the night to prevent fire breaking out… One line was connected to earth through a 2mm thick copper wire, which at once got red hot, corresponding to a current more than 10amps.”

Now telluric currents aren’t all bad.  In fact, they’ve recently been used to map and explore underground structure.  By taking measurements of voltage and current along an array of points at the earth’s surface, scientists can characterize the conductivity of different areas of the ground.  This method can even be used to identify mineral or petroleum deposits.  For more details on this, see this article on Magnetotellurics.

An example of data produced using the methods of Magnetotellurics

Well as you may have guessed, naturally-occuring telluric currents can even be harnessed to provide electrical power.  Of course, this requires a wire of substantial length.  And this point, combined with the fact that there’s not much energy to be drawn from most telluric currents anyway, makes this an impractical power source.  However, there is one related invention which at least solves the length issue: the earth battery.  Basically, the earth battery works just like any other chemical battery – you insert two electrodes made of different metals into the ground, and the earth acts as your electrolyte.  The ground needs to be slightly wet for this to really work properly.   But with such close spacing, you’re not really deriving energy from the earth’s magnetic field, you’re just making a simple chemical battery (like that potato battery you made in elementary school).  However, earth batteries did work well enough to power some early telegraph stations.  If you’re curious, here’s the patent for an improved earth battery, issued in 1874.

By the way, in researching for this article, I ran across a (seemingly) amazing “patent” for a device that claims to be able to produce 3000W of electrical power from a 500W input.   It says this can be accomplished through a simple high-frequency oscillator and a half-mile antenna which derives energy through resonance with telluric energy.  Now, I’ll let you come to your own conclusions, but I think this is bunk.  For one thing, US Patent #253,765 is for a portable fence, not an electrical power accumulator (and I couldn’t find this “patent” via term searches).   But secondly, how could telluric currents possibly resonate at 500kHz?  Everything I’ve read describes naturally-occuring telluric currents as having periods on the order of, at shortest, minutes.  Which means we’re talking about frequencies in the millihertz, not kilohertz.  In fact, most telluric current oscillations are diurnal, meaning they follow a daily, 24-hour cycle.  Oh and third, the rest of the website hosting that “patent” is unbelievably sketchy…

Anyway, if you’re curious, take a read through this chapter, available for free online, and tell me what you think.   I’d absolutely love to try this out sometime.  Anyone have any suggestions for how to do it?  I’m thinking of just buying the cheapest, longest length of wire I can get from Home Depot, along with a couple of pieces of re-bar.  Then I’ll just go find a field somewhere, set my two electrodes pointing north and south (as that seems to be the predominant direction of telluric current flow in the US), then check it with a voltmeter.  Perhaps nobody would mind if I tried this at a park someplace… 🙂

Better Than Watching Paint Dry

Quick, what’s made of glass, filled with tar, and is considered by the Guinness Book of World Records to be the longest continuously-running laboratory experiment?  No, this isn’t a memorial for the Gulf Oil Spill; it’s the famous Pitch Drop Experiment!

University of Queensland Pitch Drop Experiment (battery for size comparison)

Seriously, this is no joke (although it did win the Ig Nobel Prize in October of 2005).  This test was designed by Thomas Parnell, a professor at the University of Queensland in Brisbane, Australia, to measure the viscosity (resistance to flow) of tar pitch.

Back in 1927, Professor Parnell heated a bit of pitch (which is normally fairly solid and brittle) and poured it into a sealed glass funnel.  It was then allowed to settle for three years.  (This probably constitutes another record for the longest experimental setup.)  In 1930, the funnel was opened and pitch came bursting forth at the astonishing rate of roughly one drop per decade.  That’s a frequency of, uh, about three nanohertz.

Professor Parnell died in 1948, having only seen two drops fall.  Actually, to be clear, no one has ever actually watched a drop fall.  Despite being monitored on a webcam, the most recent drop was not captured due to technical problems.

The results?  Well obviously it’s still a work in progress – there’s enough pitch in that funnel to last for another hundred years or so.  However, the data so far indicates that tar pitch has a viscosity 100,000,000,000 times that of water.  That’s one tough fluid.

So if you’re looking for more exciting science experiments that’ll run for longer than you’ll be alive, check out Oxford’s Electric Bell and the Beverly Clock.  Good times, good times.

Computers: The Early Days

The other day I came across an old CompuAdd magazine from the summer of 1992. One word: wow. Guess how much hard drive space you’d get for $2000 back then: only 630MB. Today I get about 12 times that amount for free with GMail. But back then, the average user couldn’t even buy 1GB in a single drive. If it were possible, such a drive would’ve cost about $2500. Today, you’ll pay about $0.10/GB for a drive with platters. And people complain about the cost of solid-state drives! They’re still 800 times less expensive than standard drives from 18 years ago – and ludicrously fast by comparison.

CompuAdd Magazine Cover - Summer 1992
Yes, the early 90s, the era of 486 power and built-in math coprocessors – I barely remember it anymore. This was a time when “Realtime clock/calendar” was included in a PC’s list of features, right alongside “4MB DRAM – expandable to 64MB!” This was a time before USB, before digital cameras, and before high-speed internet. There was dial-up though, but back in 1992 most computers could only handle connections at 9600bps – that’s 1.17KB/second. Just downloading the header image on this blog would’ve taken about one minute and twenty seconds.

CompuAdd Catalog Pages 24-25Intel Overdrive ProcessorMy family’s very first computer was bought from this old magazine – a rugged 486 box complete with a blazing-fast 33Mhz processor. That’s fully 6% of the clock speed of my current cell phone’s CPU! Ah, but never fear, with the Intel OverDrive Processor, “obsolescence is a thing of the past!” Just snap this baby in when you’re ready to upgrade and boost performance by up to 70%. And for the right price you could even take your 486 powerhouse on the road. Just $2600 would make you the proud owner of a CompuAdd 425TFX laptop, complete with an 80MB hard drive, 25Mhz processor, 4MB DRAM, and a 64-level grayscale display! Now I’m not sure what the battery life might have be on one of these devices, but I doubt it was all that impressive. Most of the desktops back in ’92 were shipping with 300W power supplies – still not an uncommon size in today’s PCs.

CompuAdd Catalog Pages 12-13Want to hear something really interesting? None of the prices I’ve listed so far have been adjusted for inflation. So paying $2600 for a laptop back in 1992 would be about like spending $4000 today. Well, it’s tough to live on the bleeding edge.

And whatever became of CompuAdd? After a less than successful foray into retail superstores in the late 80s and early 90s, CompuAdd shut its doors in 1993 and filed for Chapter 11 bankruptcy protection. They did briefly continue product development, but in 1994 were acquired by a private investment group. Based on one article, it sounds like they failed because of pressure from competitors like CompUSA (who’s now struggling to keep its own stores open) and Dell. While Dell was raking in money from its public launch in 1988, CompuAdd was struggling with loans to pay for expansion. Interesting stuff if you’re into business and economics (my minor as an undergrad).