It is the year 1634, and the Voice of America is on the air. Since the VOA is an AM (amplitude modulation) radio station, speech and music are encoded as fluctuations in the amplitude (intensity) of a radio-frequency carrier wave. The radio waves, emanating from the Great Stone Radio Tower, spread across the German countryside, and enter the long receiving antennae of hundreds, perhaps thousands, of makeshift crystal radio sets.

There, they set the free electrons of the antenna into motion, dancing back and forth in response to the reversals of the electromagnetic field. That is an alternating current, and it is "rectified" into a direct current (flowing in one direction only) by a device called a diode. It is the crystal, probably a galena (lead sulphide) crystal, which serves as the diode. A capacitor (a device stores and discharges electrical energy) filters out the carrier signal, pa.s.sing only the electrically encoded audio signal. Finally, an earphone transduces that signal into sound.

The Voice of America is not the only broadcaster, and if you want to hear it, and not the Voice of Luther, you need a tuning circuit. The tuning circuit has both an inductor (a coil) and a second capacitor.

(At least one of these must be variable for tuning to be possible.) Capacitors (also called "condensers") are one of the most basic of electronic components. Their most fundamental electrical characteristic is their capacitance (ability to store electrical energy).

So how do you make a capacitor? The simplest one consists of two parallel conductive plates, and an intervening "dielectric." You can actually use a stack of plates, not just two, but the conductive and dielectric layers will alternate. One wire will be connected to the "odd-numbered" plates, and a second wire to the "even-numbered" ones.

It turns out that mica is probably the best dielectric material which is likely to be available in the years immediately following the Ring of Fire (RoF).

The Great Stone Radio Tower was built to trick the other European powers into thinking that long-distance radio requires ma.s.sive antennas. ("Radio in the 1632 Universe,Grantville Gazette, Volume One). This bit ofmaskirovka was successful for only a limited time. By March 1634, the Cavrianis had figured out that the Venetian Emba.s.sy was in radio contact with Grantville. (1634: The Galileo Affair,Chap. 27). It is only a matter of time before the French and other governments realize the American capabilities, if only by inference from the celerity with which the USE acts.

Those powers will quickly appreciate the advantages which would accrue to them if they, too, had radio communications for diplomatic and military purposes. We can expect that collecting information on electronics in general, and radios in particular, is going to be a fairly high priority for the mult.i.tude of spies in Grantville and Magdeburg.

The knowledge of how to build crystal radio receivers is being widely disseminated ("Waves of Change,"Granville Gazette, Volume Nine), so the focus will be on finding out how to build suitable transmitters. Details appear in another article in this issue ("Radio 3:Grantville Gazette, Volume Nine), but the simplest transmitter would be of the "spark gap" type. This can send Morse code, but not music or speech.

Now it turns out that any spark gap transmitter will need at least one capacitor that can handle high voltages. To survive the high voltages, the capacitorsmust use mica as the dielectric.

Mica is less critical insofar as receiver capacitors are concerned, but a receiver employing mica will have greater sensitivity than one using an alternative dielectric. That is important if you are on the fringe of the broadcast area.

While spark gap transmitters will initially be used by foreign governments, it is only a matter of time before the knowledge of how to make them is pa.s.sed on to others, such as merchants. The Cavrianis used the American radio to advantage in the futures market, and their counterparts will be quick to perceive the benefits of acquiring their own radio capabilities. * * *

As the ability to receive a radio broadcast spreads, other political groups-some hostile to the USE-will want to make sure that they can speak to the radio audience. And there will be other broadcasters, whose interests are economic rather than political.

To actually "speak," you need a radio transmitter which can simulate a continuous wave. The Voice of America's transmitter is a rebuilt, high-powered, "ham" radio outfit, while the Voice of Luther will broadcast from a "Fessenden Alternator" constructed with down-time materials ("Radio in the 1632 Universe,"Grantville Gazette, Volume One). I a.s.sume that the Fessenden Alternator will initially be beyond the capacity of down-timers lacking direct USE technical a.s.sistance.

The most likely alternative would be a variation on the Poulsen arc transmitter, which combined an arc lamp, a coil, and a capacitor. Like the capacitor of the spark gap transmitter, this one needs to endure high voltages.

Of course, some folks won't want to broadcast themselves, but will be keen on jamming the transmissions of others. Capacitors can be used in radio jammers, too. ("Little Jammer Boys,"Grantville Gazette, Volume Nine).

It is time now to take a closer look at why mica is so desirable for capacitor construction. Mica, to begin with, is an insulator. All insulators can be used as dielectrics, but they differ in terms of their ability, per unit thickness, to separate charges (and thereby store energy). The measure of that ability is the dielectric constant. The dielectric constant of mica is about 49; of common materials, only gla.s.s is superior (about 510).

Another important characteristic is dielectric strength. If too great a voltage is applied across the plates of a capacitor, the current will force its way through (this is called "breakdown") and may arc-weld the plates together. Higher voltages can be tolerated if the dielectric layer is made thicker, but that reduces capacitance. Hence, high voltage capacitors are usually made of materials with a high dielectric strength (a measure of the ability of a material, per unit thickness, to resist arcing).

Mica has superior dielectric strength (5,000 kV/inch, versus 2,0003,000 for gla.s.s). So a thin mica capacitor can resist a high voltage. Having a high dielectric strength is particularly important if you are constructing a transmitter capacitor.

When a voltage is applied to a capacitor, charges build up on the plates, but some of the electrical energy is lost as heat. Ideally, the capacitor has a low dissipation factor. The dissipation factor for mica is .0003.0004 for mica, versus .01.05 for soda lime gla.s.s. (Eccosorb) Thermal stability (how much does the capacitance change if the temperature changes?) is also of interest if the capacitor is being used outdoors or in unusual environments. For mica, "Capacitance will change only -2% at -54C, and to +3% at +125C. " (McCloskey) Mica has other great properties, too. It splits readily into very thin, flat sheets, which are flexible, heat-resistant, chemically inert, and, in some cases, transparent. The latter property led to its use in house windows in Russia ("muscovy gla.s.s") and in oven windows in the United States ("isingla.s.s").

Jason Cole of the University of Waterloo writes, "When it comes to modern technology, sheet muscoviteis an indispensable resource. It is used in almost every electronic device sold today as an insulator. Its high resistance to the pa.s.sage of electricity and heat are so great that no subst.i.tute, artificial or natural, have proved to be economically suitable to replace it. No other mineral has better cleavage, flexibility or elasticity. It is possible to roll a sheet of muscovite less than 0.1mm thick into a cylinder 6mm thick and its elasticity would enable the sheet to flatten out again quite easily. Sheet mica is just as important to the electrical and electronic industries as copper wire and now ranks as one of the essential minerals of modern life."

Mica So what is mica, exactly? It is a group of aluminum silicate minerals. The two most important species for the electronics market are muscovite mica and phlogopite mica.

Muscovite micas are divided into the ruby and green varieties, based on color. The term "ruby muscovite" includes the clear forms.

Phlogopite micas are "rarely found as colorless transparent sheets"; they are sometimes called "amber"

micas. Rouse (352) says that they can't be used for capacitors because their power loss is usually over 1%, whereas the maximum permissible losss is 0.04%. They tended to be used in OTL mostly for high-temperature applications. Cole says that "Muscovite mica cannot be used in temperatures that exceed 550 degrees Celsius, whereas, phlogopite can be utilized at temperatures up to 1000 degrees Celsius."

Commercially, mica is cla.s.sified according to its thickness, size and appearance. (Paramount; Rouse, 3401).

The term "block mica" tends to refer to large, thick pieces (at least 7 mils, one mil is one-thousand of an inch) which can be split and trimmed into useable sheets.

Sheet mica is at least 1 1/2 by 2 inches in size, and thinner (say, 17 mils) than a block. The thinner sheets, if of high quality, are sometimes referred to as "film."

The term "splittings" refers to pieces which are smaller than the smallest standard sheet, but at least 0.75 square inches in area. They are usually thin, too, perhaps 12 mils. Below that size we have waste or sc.r.a.p mica, sometimes divided into flake mica and mica powder.

It is possible to a.s.semble splittings into what is called "built-up" mica. Also, mica flakes and powder can be be used to make "reconst.i.tuted" mica ("micanite").

Micanite was invented in 1892 (Rajgartha, 4). Micanite is described in EB1911 as consisting of "small sheets of mica cemented with sh.e.l.lac or other insulating cement on cloth or paper." That is probably a sufficient description for the up-timers to duplicate it, if need be.

Paramount says that "the dielectric material used in the production of mica paper capacitors is reconst.i.tuted mica paper that is impregnated with a polymer resin." Nonetheless, the preferred material for capacitor dielectrics is certainly sheet mica. Chowdhury (257) says that "the highest quality mica, absolutely flawless, is required for radio and wireless purposes." (See also Rouse, 343). And Rouse(376) says that "the power loss shown by the bentonite films [for built-up mica] . . . is too high for them to be used in condensers . . ."

The quality rating of mica seems to have gone through many changes. Depending on which references you consult, there are anywhere from twelve to twenty possible rankings. The ASTM presently uses twelve (V-1 to V-7, V-7A, then V-8 to V-10A), which range from "clear" to "densely black and red stained. " I would expect, based on another source, that only V-1, V-2 ("clear and slightly stained"), V-3 ("fair stained") and V-4 ("good stained") are considered "capacitor grade. " (Misc. Diel.) http://my.execpc.com/~endlr/misc__dielectrics.html We may be less picky in 1632, of course. Especially for receiver capacitors (USGS). The lesser grades of mica can, of course, be used as insulators, and that is a major use of micanite.

Mica Sources Reported in USE Reference Materials As is too often the case for raw materials needed by the USE, the best known, most prolific sources of sheet mica are far away. We may have to pa.s.s through enemy spheres of influence to reach them; they may even be under enemy control.

So where do the encyclopedias direct us? EB1911 "Mica" says that muscovite sheets are found in India, the United States (South Dakota, Colorado and Alabama), and Brazil (Goyas, Bahia and Minas Gerais), and phlogopite in Canada and Ceylon.

The other Grantville encyclopedias don't distinguish between muscovite and phlogopite. The sources they list are:

Encyclopedia Americana: India, Madagascar, Brazil, USA (New Hampshire, North Carolina, South Dakota)

World Book Encyclopedia: India, Brazil, Madagascar, USA (North Carolina, New Mexico, South Dakota)

ModernEncyclopedia Britannica : India, South Africa, Soviet Union, Brazil, Argentina, Canada, Madagascar, USA (North Carolina, Idaho, South Dakota)

Collier's Encyclopedianotes that "the United States is the largest producer of bulk mica, but the greater part of the capacitor grade mica is mined in India." It adds that two-thirds of the American production was mined in North Carolina. The encyclopedias provide no quant.i.tative information. However, for the sake of the story writers, I will give a few numbers. The leaders in sheet mica production in the period 19131937, ignoring the secretive Soviet Union, were India (236,916,000 pounds, 74.6% of world production), United States (10.1%), Canada (4.8%), Madagascar (3.6%), Argentina (3.5%), Brazil (1.9%), and Rhodesia (1.4%).

(Rouse, 349) In 2000, the largest producers were India (3,500 metric tons) and Russia (1,500)(USGS).

Prospectors are not, of course, limited to the known mica locations. However, without some kind of lead, the discovery of mica will be quite chancy.

Russian Mica Russia, of course, has mica: the term "muscovite" is something of a giveaway. According to the Oxford English Dictionary, the term "Muscovy gla.s.s" was used in English to denote sheet mica at least as early as 1573. In 1604, J. Marston made reference to the ease with which thin sheets could be split off a mica "book" ("She were an excellent Lady, but that her face peeleth like Muscovy gla.s.s.") Hooke's Micrographica (1665) refers to the unusual optical properties of thin sheets of "Muscovy gla.s.s" (sheet mica from Russia).

What practical use was made of it? Mica sheets could serve as the clear but heat resistant panes of a lantern. T. Dekker, in 1606, referred to "a candle in a Muscovy lanthorn." They could also be used in more conventional windows. K. Digby noted in 1644 that the windows of his cabin were made of Muscovy gla.s.s.

It is clear from the foregoing that, by 1632, mica had been discovered in Russia, and exported to other countries. I don't have any economic data for the early seventeenth century, but in 1681, Russia exported 92,882 pounds of mica to Holland, 86,400 to England, and 18,000 to North America. (Chowdhury, 178). I have no idea what percentage of this was sheet mica, but the most likely use of the mica was in windows, and that would have required transparent (or translucent) sheets.

The Russians used it mostly as an "upscale" window material. In the late 1660s, Tsar Alexei Mikhailovitch had a summer palace built at Kolomenskoe, near Moscow. It had 3,000 mica windows.

Where does the Russian mica come from? TheHammond Citation World Atlas , which most likely made it through the RoF, contains an economic map of Russia and, lo and behold, identifies mica localities. I pity whoever goes to the Atlas' European Russian site; it is a little west of the far northern town of Kandalaksha, in Karelia. There are four mica localities shown to exist in Asiatic Russia, two of which are in the general vicinity of Irkutsk.

Fortunately, we don't have to find the mica ourselves, we just have to trade for it.

Indian (and Ceylonese) Mica The encyclopedias consider India to be the premiere world source of muscovite sheet mica, so it is reasonable to consider it more closely. According to Brown (541), "the date of the commencement of mica mining in India is lost in antiquity."

However, it is unclear which of the current mica fields were known in the early seventeenth century.

Of course, we can give our Indian trading contacts some hint as to where to look, if need be. EB1911 says that mica is mined in Haziribagh (Bengal) and Nellore (Madras), and a prominent Nellore mine is "Inikurti."

I have also studied the economic map of India in the Hammond Citation World Atlas. To avoid inadvertent bias, I compiled my list of mica localities from the Atlasbefore examining even the encyclopedias, let alone any of the professional geological texts. I would estimate that the Atlas can be used to localize mica sites with an accuracy of perhaps 2550 miles. The greatest is in Bihar, close to Hazaribagh. A second is also in Bihar, at the same longitude as Asansol, but north of the Ganges River.

Monghyr, on the south bank, is nearby. The third is in Andhra Pradesh, near Nellore. That is all that the up-timers will know.

The USGS says that in India, "mica mines are operated in the States of Bihar, Andhra Pradesh, and Rajasthan. In Rajasthan, the princ.i.p.al mines are at Banjari, Barla, Bhojpura, Chapi, Galwa, Ganeshpur, Ghegas, Laxmi, and Sidiras. " An Indian government report says, "the main mica-sites in Andhra Pradesh are found at Atmakur, Ravuru and Gudur of Nellore district. Large deposits of Mica are also found at Tiruvuru in Krishna District, Madhira [Khammam District], and Ankannagudem of West G.o.davari, all in AP. " (MMPIndia) * * *

The importation of mica sheets from India will be much easier if, by the early seventeenth century, it was already an article of commerce, something our traders could just ask for. Gathering information on this issue has been something of an exercise in frustration.

Mica (Hindustaniabrak , fromabr cloud orabru the heavens) was used in ancient Indian medicine. The medical use of mica was probably of mica powder. Those who sell the medicines, or even the powders, may not know how to obtain the mica sheets. So it would be better to identify trade goods in which the mica sheets are used in intact form.

The mineral supposedly has been employed "from time immemorial, for ornaments, decorations and glazing, as well as by artists for their transparent paintings. It finds a place in the tinsel decorations of banners, taziahs and umbrellas at festivals and weddings. Its powder is sprinkled on clothes, fans and toys, as well as being incorporated in the glazes of some forms of pottery. . . ." (Brown, 541).

Chowdhury (6) says that the "early" use of mica was in medicines, ornaments and vestries for idols, decorating, glazing or transparent mediums, and as a painting base (ground).

Like Brown and Chowdhury, EB1911 notes that sheets of mica have been used in India as a surface for painting. However, I believe that this began only after India came under British rule. (Swaveda, Chennai).

A computer search in the Mina.s.sian Collection of Persian, Mughal and Indian Miniature Paintings turned up six mica paintings, all of which were dated as "Company School." Likewise, Swallow, Arts of India: 15501900 refers only to "Company" paintings on mica, not to Mughal works of this type.

Still, Swallow offers some hope. He claims that mica was "originally used for festive lamps and the illuminated windows of thetaziyas , elaborate model tombs carried by Muslims in the Muharram festival processions. . . ." One of his sources (Skelton) says that according to a contemporary account, "artists were employed to paint sheets of mica for the festival lamps at Murshidabad in the reign of Murshid Quli Khan." Murshid was the nawab of Bengal 17061725. I think it is reasonably likely that mica was known to Indian merchants of our period, especially those familiar with the Bengalese towns of Trichinopoly, Patna, Murshidabad and Benares.

While India is known for muscovite mica, Ceylon is a source of phlogopite. "In Ceylon, the mineral forms irregular veins, rarely exceeding one or two feet in width, traversing granulite, especially near the contact of this rock with crystalline limestone." (EB1911, "Phlogopite") Unfortunately, the Hammond Atlas doesn't reveal the location of the Ceylonese deposits.

New World Mica In the United States, we can find mica in several states. Mica resources are identified on the Hammond Atlas economic maps for Alabama, Colorado, Connecticut, Georgia, Maine, New Hampshire, North Carolina, South Carolina, and South Dakota. There was low-level collection and trading of mica by the American Indians in pre-colonial times. For example, North Carolina sheet mica, cut into the shape of a hand, was found at Hopewell site in Ohio. The artifact is from AD 1400.

However, to acquire significant supplies of mica, we would have to rediscover the OTL sites and mine the mica ourselves.

The EB1911 article on "Phlogopite" adds that "in Canada it occurs with apat.i.te in pyroxene rocks which are intrusive in Laurentian gneisses and crystalline limestones, the princ.i.p.al mining district being in Ottawa county in Quebec and near Burgess in Lanark county, Ontario." The Hammond Atlas map for Quebec shows mica west of Montreal and north of Ottawa.

In South America, Brazil and Argentina are both mentioned by the encyclopedias. According to the Hammond Atlas, in Brazil it is found northeast of Rio de Janeiro and Belo Horizonte. It doesn't map out the Argentine sites.

African Mica Madagascar is famous nowadays as a source of phlogopite mica. Despite Rouse's criticism of phlogopite as susceptible to high power loss, if we can't obtain muscovite mica in quant.i.ty, we might need to make do with phlogopite.

According to the Atlas, the Madagascaran mica is near Faradofay (Fort Dauphin), in the southeast. I suspect, from the lack of any reference to it in EB1911, that it was not discovered until later in the twentieth century. If so, then the only way to obtain Madagascar mica is probably to send prospectors and, once they are successful, set up a mining operation.

As of 1632, there was no major European presence in Madagascar; there may be scattered missionaries. Control of the island is divided among several small kingdoms.

* * *There are three mainland African mica sites: near Louis Trichardt in the Northern Transvaal (South Africa), in Tanzania, south of Lake Rukwa, and in Zambia, south of Chipata. The first of these is probably the one contemplated by the modern EB.

Australian Mica Close study of the Hammond Atlas would reveal that there is mica in the area north of Alice Springs, Australia. Since that is in the hostile Australian Outback, it is unlikely to be investigated (except perhaps as a sideline to gold prospecting somewhat further north).

Mica in Friendly Territory So is there mica in friendly territory, that is, in USE-controlled Germany, Sweden, Finland, and the Swedish-controlled Baltic coast? Not to the knowledge of the people in Grantville. Sadly, the atlas offers no clues as to the whereabouts of mica occurrences in Europe, other than in Russia.

But yes, there are modest mica deposits in those areas. Rockhound databases (Mindat) can provide a long list of German, Swedish and Finnish localities where muscovite mica can be found. That, of course, doesn't guarantee that sheet mica can be extracted in a commercially feasible manner.

Just so the storytellers of the 1632 universe know where mica could in fact be found, I have consulted some specialist up-time texts. The results appear below.

Germany. Chowdhury (183) a.s.serts that Germany produces lithia mica (lepidolite) but no sheet mica.

And Rajgartha (104) confirms that there is no "primary production" in West Germany. A 1945 U.S.