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 worked. 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 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 "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 removing 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.
Another side note: This is the last kit remaining in Gakken's Otona no Kagaku mook series that was still in print that I hadn't reviewed yet. There are 5 other kits that I haven't built (the pinhole camera, crystal radio, early microscope, steam-powered toy car and da Vinci's helicopter) but that's because they're out of print and too expensive to buy from collectors off of auction sites. I may get one or two of them if the price comes down, but they're not on my radar right now. The next kit from Gakken, #25, will be the reflex camera at the beginning of October. I may buy that just to have a way to use up some 400 ASA film that's too fast to be used in the stereo pinhole camera, but #25 isn't something that really interests me right now. In the meantime, I'm waiting to see what #26 will be, and I'm preparing to make a video showing my synth keyboard and other silly stuff at work all at the same time.