Kit 22: Gennai Hiraga’s Electricity


Kit #22, Gennai Hiraga’s Electricity (2500 yen ($25)). Again, we have a famous Japanese inventor that few people outside of Japan know about, and a kit that could have been a lot of fun if it lived up to its potential.

According to wikipedia, Gennai Hiraga was a pharmacologist, physician, author, painter and inventor who lived during the Edo period (1729 to 1779). He had access to western books and artwork, which he studied and built on. His forays into electricity included the development of an electrostatic generator, and he also created a thermometer and an asbestos cloth. Apparently, he tried to get new mines opened up locally so that he could study various ores, and his frustration over the lack of support from the government caused him to go into a rage, resulting in his killing one of his students. He was then arrested, and he died in prison. Gennai has been used as a cameo character in various anime and video games, including “Read or Die”.

If you’ve ever played with a glass rod and silk cloth to create a spark, then you know how Gennai’s generator works. In essence, it’s a roller connected to a handle, and the roller rubs against a cloth to build up a charge, The charge is stored in a kind of Leyden jar until it builds up enough to overcome the air dielectric between two electrodes to create a spark. For each 1 mm of air gap, you need about 1 kV potential to make the spark (5 mm would represent 5 kV). According to the Gakken mook, Gennai drew pictures of people holding hands in various party games to pass the electric charge through the group and make their scalps tingle.

The Gakken kit is a modern variant on Gennai’s design. The plastic case is 3″ x 2″ x 2″ and the sides snap together, although they’re also intended to come apart easily to allow for modifications as desired. Inside, a plastic roller sits on top of a sheet of cotton which is also on a metal plate. A charge collector plate is about 1mm to the side of the roller. Both plates are connected to steel wires that are brought up to a capacitor. The capacitor is then connected by springs to the electrodes on the top of the box, where you can adjust the air gap to get a longer or shorter spark (3-5 mm). The capacitor is a plastic sheet with two sheets of aluminum foil tape stuck on both sides. The capacitor increases the surface area for the charge to build up on and takes the place of the Leyden jar. For lubrication of the ends of the roller where it contacts the box, the mook suggests either regular machine oil or light salad oil.

There seem to be quite a few ways that this kit can fail to work. The oil can get on the barrel surface of the roller, the gap of the collector plate can be too big or small (the roller is slightly off-center so the plate can easily come in contact with the roller by accident), the air can be too humid, the springs holding the capacitor plate in place may not be touching the foil tape to complete the circuit, etc. Gakken has a video clip showing the kit working, and even when everything’s set just right, the spark’s not all that impressive.

Suggested mods to the kit are to add a second “Leyden jar” to boost the charge further (two plastic cups wrapped in foil); to place a sheet of foil on the collector plate to touch the roller to increase charge collection; to put a metal ball between the two electrodes to create an oscillating pendulum; and to replace the electrodes with 2 plates and put a disk in between them to recreate Benjamin Franklin’s static electricity motor.

The mook explores Gennai’s accomplishments while explaining the principles behind the static generator. There are pictures of his drawings and paintings, a short biography and a timeline. Other articles include the history of electricity research in Japan up to the 1800’s; contest-winning photos of different types of lightning; a story on the world’s largest Van de Graaff generator; a how-to for playing Gakken’s Premium Theremin kit; and other pieces regarding electricity and the human body. There’s also a how-to for building Lord Kelvin’s dripping water charge collector and a piece on an amateur-built Wimshurst machine. The mook is a great resource for information on static electricity, suggestions for experiments and for information on Gennai. And the photos of lightning are really good.

The problem is the kit itself. If it doesn’t work, it’s really hard to troubleshoot because you keep having to disconnect the wires and remove the capacitor plate to open the box, and by then the circuit’s disassembled. Having an ohmmeter and some jumper clips is a good idea, just for confirming continuity of the wiring. The reason my kit didn’t work is because the oil spread between the roller and the box wall, creating a conductive path to bleed the charge off the roller, and an ohmmeter won’t catch that (I took the kit apart, removed most of the cellophane tape and cleaned all the oil off with rubbing alcohol, and that fixed part of the problem). Even when it is working, the spark isn’t that big. But, the kit looks good on the shelf with the painted paper sheets glued to it, so it does rank up there with the phonograph and Stirling engine kits as conversation pieces. However, if you want to teach children the principles of static electricity, this is a good kit to start with (assuming that you can make it work).

As a side note, the ads in each of the mooks tend to be related to the topic of the mook. In the case of kit #22, one of the ads was from TEPCO (Tokyo Power and Electric) for their Electric Power Historical Museum, located a few minutes away from Kawasaki station, in Kawasaki City.

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The other day, I was in the bookstore in Noborito train station when I noticed a new Gakken kit that was obviously familiar. There was a TV drama series on in Japan called “Trick“, which teamed up a physicist and a stage magician to debunk fake spiritualists. Well, apparently the show’s producers paired up with Gakken on the static electricity generator. It’s the exact same kit as before, but with new labels from the show to stick on the case, a slimmed down mook, and a picture of the professor character on the box. Oddly, I can’t find an image of the new box on either the Gakken site, or on Amazon.jp. One big difference, though, is that the “Trick” version is 1900 yen compared to 2500 yen for the regular kit. (I apologize for the photo. When the cell phone made the clicking sound a nearby shop clerk stood up really fast and I wasn’t able to try to get a better image.) The slimmed down mook contains the same static electricity experiments as the original, plus some photos of the Trick actor in his professor character explaining the science behind the kit.

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The Tepco Museum

One of the fascinating things about living in Tokyo is the skewed sense of distance that it provokes. Many people have cars here, and they clog the roads trying to get around the city. Partly as a result of wanting to avoid the congestion, partly because gas is about $6 a gallon, and partly because many people don’t want to bother with taking care of a car, most people travel by train.

From my apartment to the northeast, Shinjuku, the west side of what’s typically considered to be Tokyo city, is about 20 minutes by train. To the southeast, Kawasaki is about 20-30 minutes and Yokohama is about 10-15 minutes past Kawasaki. Most of the Tokyoites I talk to make a big deal about how far away Yokohama and Kawasaki are. But it’s really only 15 miles to Shinjuku from me, 15 miles to Kawasaki and maybe 22 miles to Yokohama (all numbers are approximate and off the top of my head). The reason the train takes so long is that it has to stop every mile or so at a station and wait 1-2 minutes for the passengers to change, and that the train’s top speed is about 30 mph. If you have a book or listen to music, the ride’s not that bad, but most people just don’t want to take the 1 hour to make the trip.

Where the skewed sense of distance really kicks in is when you get on a bicycle on a good stretch of bike path (the trail along the Tama river near me is great leading west all the way out to Takao. It’s not so good for half of the southeast stretch to Kawasaki and it doesn’t reach Yokohama). I can get to the Kawasaki museum in Todoroki in about 15 minutes. The Kawasaki train station is another 20-25 minutes after that and part of the ride is on sidewalks in the major shopping districts (lots of foot traffic there). I haven’t tried getting to Yokohama yet, but it’s doable once you get 1-2 miles past Kawasaki station. That is, if you have a good bike and a good stretch of trail, a lot of interesting places in and around Kawasaki and Yokohama aren’t that far away.

Why bring all of this up? Well, as mentioned above, there’s an ad at the back of the Static Generator mook for Tokyo Power Company’s (TEPCO) Electric Power Historical Museum. The TEPCO museum is 5 miles the other side of Kawasaki station, and when I mentioned that I may ride to Kawasaki, I was met with looks of disbelief that I’d want to travel that far. But, it only took 40-50 minutes, and only part of that included cutting through foot traffic around Kawasaki station. Mostly, it was a nice, pleasant form of exercise.


(Berliner’s early flat record player.)

The TEPCO museum isn’t that easy to find, even with a map (since their map’s not to scale), being tucked away between a residential area and a wide swath of train tracks. The museum itself is in a sprawling 2-story building housing a cafe, gift shop, exhibit areas and some theater space.

They advertise having 700 items on display, and that number’s probably about right. Many of the smaller items are just high voltage insulator parts, motors, huge bolts, transformers and snow shoes (there’s a ski and snow shoe display because the power company construction people had to travel by foot to put up the power lines through the mountainous regions of central and northern Japan). But, they also have larger antique items, including power towers, refrigerators, Edison and Berliner phonographs, turbines and power station control switch banks. Their pride and joy is an 115-year-old original electric car, which pre-dates Ford’s model T gas-powered car by several years. The electric car came from Edison, but didn’t become popular because the lead batteries of the time took too long to charge, and had a limited range.

The museum is set up chronologically, starting with a display of Europeans (Volta, Ampere, etc.) that laid the foundation for understanding electricity, through an orientation film on Japanese electrical history, to Tokyo’s first power grid, the Great Kanto earthquake (which forced Tokyo to re-lay out the grid from scratch) up to TEPCO’s modern day technology. It’s all really cool, and the 3-story turbine blade is full-scale. Also, they let you take pictures. In fact, while I was there, a photographer and his model were shooting the various exhibits for use in an elementary school textbook. After I was done wandering around, I stopped at the cafe for a hot dog, yogurt with blueberry syrup and ice coffee. Then I went to the gift shop, where they carried lots of science books, toys and bento lunch boxes with the TEPCO mascots printed on them. I wasn’t too surprised to see that they also sell two of Gakken’s kits – the spark generator and the theremin (side note: the pictures of Gennai Hiraga in the Gakken kit book probably came from TEPCO, as many of the same photos are on display in the museum).


(Cut away of a Japanese heated toilet.)

If you’re in Kawasaki, it’s worth visiting the TEPCO electricity museum. It’s only 300 yen ($3) for adults.

My full photo album is here.

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