In part 3, I talked about deck, cabin, and hold illumination. But there’s also a need for lighting by which the ship sees what lies around it, and is seen in turn. Lighting may also be used for communication, ship-to-ship and ship-to-shore.
Stern Lanterns. When ships were traveling in formation at night, there needed to be a way for the helmsman on one ship to see the ship in front of him (rear-end collisions and meandering off both being frowned upon). Hence, sailing ships carried stern lanterns (Laughton 159). This practice was not limited to warships as, in the seventeenth century, European trading ships often sailed with escorts.
In Edward III’s navy, the number of stern lanterns indicated the status of the commander; three or more for the King, two for the admiral, and one for the vice-admiral (Traill 186). On sixteenth-century Venetian galleys, those commanded by a squadron commander had a single stern lantern, and the flagship of the Capitano Generale da Mar or the Provveditore Generale da Mar had three. Indeed, the flagship was sometimes referred to as a lanterna (Motture).
The 68-gun warship La Couronne (1626) had three lanterns above the taffrail; the center one was 12 feet high and 24 feet in circumference illuminated by twelve pounds of candles. (Sephton). On the Sovereign of the Seas (1637) there were five lanterns on the stern (Sephton 57, 61) , two apiece on the port and starboard quarter galleries, and the fifth and largest on the aft end of the poop above the taffrail. It was six or seven feet high, and four to four and a half feet wide. In 1661, Samuel Pepys, then clerk of the Naval Board, gave a tour of the Sovereign to his patron’s wife, Lady Sandwich, the Lady Jemimah, and their seven companions and servants, and persuaded this tour group to join him in squeezing inside the stern lantern (Dill 12)—plainly the seventeenth-century equivalent of squeezing into a phone booth.
While a single stern lantern reveals the position of the ship, it says nothing about its heading. But if you were looking at the stern of Sovereign, you would see three lights in circumflex (^) arrangement, whereas broadside you would see a rotated “L”. Nonetheless, this does not seem to have initiated a general trend toward use of multiple lights to show orientation.
In the early eighteenth century, all British first-, second-, and third-rates carried three lights, and this privilege was extended to fourth-rates in 1722. In 1804 it was decided that only a flagship would carry two lights, and all others just one (Willis 56). However, I believe that the second light in question was a top-lantern (see next section).
At least some early lanterns had panes of green-tinted mica, but these were displaced by glass, which rendered the light easier to see. Hexagonal and octagonal designs were the most common, but the lantern on the Merhonour (1622) was seven-sided (Howard 114). It cost over eleven pounds, not even counting the glass plate, but almost half of that was attributable to gilding (Laughton 142).
Top-Lantern. When William, Duke of Normandy, sailed across the English Channel, he “had a lantern placed at the top of his ship’s mast, so that the other ships could see it and hold their course behind him” (Musset, 196). On the 1564 Legazpi Pacific expedition, a ship in need of assistance at night would place a lantern in the main mast and fire a shot, and if it were an emergency, it also hung a lantern in the foremast and fired two more shots (Licuanan 64). In 1595, Drake ordered his fleet that if they had to unexpectedly make sail on a night that it had previously shortened sail, it would show “a single lantern with a light at the bow, and another at the fore-top” (Maynarde 64).
Later, it became customary that a British navy flagship leading a squadron would display a lantern at the aft edge of a masthead: the main top (full admiral), fore top (vice admiral), or mizzen top (rear admiral) (Lavery 255). It was supported on each side by iron braces (Falconer 294).
In 1762, Admiral Howe ordered that a ship tacking at night was to hoist a light and keep it visible until the maneuver was completed (Willis 56).
Lightships of course also displayed lanterns on high, but early lightships suspended small lanterns from a yardarm or dedicated crossarm. Robert Stevenson proposed a lantern that surrounded the mast of the vessel, and could be lowered to the deck to be trimmed and then raised back. (Stevenson 39). Presumably, the vertical traversal of that lantern would be limited by the yardarm above. It is conceivable that the lantern had a dedicated mast; i.e., one that did not ever carry sail.
In 1838, the US Congress enacted legislation providing that between sunset and sunrise every steamboat must carry one or more signal lights that can be seen by other boats navigating the same water. A three-light system was privately adopted by the Liverpool steam packets. In 1847, a different system—red on the port bow, green on the starboard bow, and a bright white light on the foremast head—was adopted for the mail steamers on the west coast of England. Finally, in 1848, a similar system was applied to all British steam vessels between sunset and sunrise. (Grosvenor).
By the 1870s, it was proposed that the masthead light be electric (Trowbridge 723). This was met with numerous objections—the ships met would be blinded by the light, the carrying ship’s side lights would be rendered inconspicuous by comparison, the ship would be mistaken for a lightship, etc. (Thomson 190).
The Titanic carried a single electric masthead light on her foremast, 145 feet above the water. It was 32 candlepower, and its Fresnel lens concentrated the light into a horizontal arc with a vertical amplification factor of 25. It thus would have been as bright as a first magnitude star at a distance of 17 miles(Halperin).
There is an obvious downside to the use of any lights on shipboard, let alone lights intended to reveal one’s presence to other vessels.. Drake ordered, “you shall keep no light in any of the ships, but only the light in the binnacle, and this with the greatest care that it be not seen, excepting the admiral’s ship . . . .” (Maynarde 64). And even today, there are waters where small boat captains don’t switch on their mast lights (Liss 62).
On the other hand, in 1800, Thomas Cochrane in the brig sloop Speedy was able to evade a frigate at night by placing a lantern on a barrel and letting it float away (Wikipedia).
Lighting the Waters: Star Shells
Sometimes it is desirable to illuminate the surrounding waters at night, in order to spot navigational hazards or enemy craft.
The star shell (“light ball”) is fired by a mortar (high trajectory gun) and contains a small explosive charge and a time fuse. The charge in turn ignites the illuminating composition. Early compositions included mixtures of sulfur, saltpeter (potassium nitrate), and realgar (arsenic tetrasulfide), orpiment (arsenic trisulfide), or antimony (Griffiths 91)
Appier’s La Pyrotechnie (1630) gives a formula for “fire balls . . . so white that one can scarcely look at them without being dazzled,” that comprises saltpeter, orpiment, gum arabic, and, strangely enough, ground glass and brandy (Skylighter).
In its original form it was not very useful at sea as the “stars” would fall into the water, and be extinguished within a few seconds. And even in land warfare, the enemy could be expected to throw water or sand over it.
Edward Boxer (1819-1898) proposed modifying this shell to be composed of two hemispheres, one containing the illuminant (“stars”) and the other a calico parachute connected to the first by ropes or chains. The explosion of the charge not only ignites the illuminant, it separates the hemispheres, but only insofar as the connector permits. The parachute slows the descent of the illuminant (Ibid.). Boxer was probably unaware that there had been experimentation during the time of Louis XIV with rockets equipped with parachute flares (Faber 181). For that matter, Congreve had a rocket light ball with a parachute (Sterling 401).
I have documented use of magnesium flares in photography of the Comstock Lode mine (1868) and the Great Pyramid (1865). I wasn’t able to determine when magnesium, aluminum, or magnalium ribbons were first used in star shells, but the first reference I found was from just before World War I (US Army, 2-11). The parachutes were also minimized, so that six or eight parachute-illuminant combinations could be fit inside a single shell.
Lighting the Waters: Searchlights
Searchlights are essentially a military development of the spotlight—that is, they combine a highly luminous source, a light concentration system, and a pivotable and tiltable mount.
In the new time line, there isn’t yet a military need for a searchlight: engagements are mostly as short range (a few hundred yards) and during the daytime. Flint and Gannon, 1636: Commander Cantrell in the West Indies, chapter 48 is the first step toward changing that; the Resolve begins firing at a range of 1800 yards, and actually scores a hit after it closes to 1100 yards.
Still, the Resolve attacked in the daytime. The biggest reason for equipping naval warships, especially capital ships, with searchlights was the introduction of the motor torpedo boat, which could launch a night attack either stealthily or at high speed.
No foe of the USE has yet (1636) built powerboats or self-propelled torpedoes. But the USE navy did have to face a smoke-screened spar torpedo attack by Prince Ulrik’s galleys during the Baltic War in 1634. Moreover, the ironclads and timberclads are intended for riparian and coastal warfare, and they could encounter mines or massed rockets.
So there is an incentive to at least start thinking about military searchlights . . . . And conceivably small searchlights would be advantageous for nighttime civilian use, too: spotting navigational hazards, rescuing men from the water or a disabled craft, and signaling.
There is a strong kinship between ship searchlights and lighthouse lights. Of course, the latter can be much larger and heavier.
Light Sources. Electric searchlights, with light generated by a carbon arc, were used at the siege of Paris (1870-1). In a carbon arc, a strong electric current is made to flow across a short air gap between two carbon electrodes. The proof of concept was made by Davy in the early nineteenth century. Grantville literature provides some design guidance (EB11/Lighting, 659-66).
The arc can be started only by bringing them in contact with each other, but then the electrodes are slowly separated. Since the rods burn away you need a mechanism to maintain the arc gap. The stability of the arc is improved by putting a ballasting resistance in series with it (which increases the power requirement).
Direct current is preferred as it causes the anode to form a crater, which gives off most of the light. The intensity is greatest at a 30-45o angle from the anode axis, and this facilitates capturing the light with the reflector (Baird). High currents (130-300 amperes in 1917) are used in military searchlights so the source must be close by.
To provide the direct current, the carbon arc light would be powered by a dynamo (a type of generator). The first dynamo was built in 1832 but major industrial use (e.g., in carbon arc furnaces) didn’t come until after improved designs were patented in 1866-7. Electrical engineers in Grantville would know how to design a good dynamo.
In NTL, carbon arc lamps are in use in Grantville in October 1633; see Offord, “A Season of Change” (Grantville Gazette 50), and at Rasenmühle in April 1634, see Prem, “Ein Feste Burg, Episode 7” (Grantville Gazette 46),
The first carbon arc lamp emitted over 10,000 lumens (Banke), and I found an ad for a 60-inch WW II carbon arc searchlight that put out 525,000 lumens (candlepowerforums). Carbon arc lamps have low luminous efficacy (2-7 lumens/watt) and efficiency (0.3-1%). Hence, they generate a lot of heat; consideration must be given to providing proper ventilation.
Now, it is worth noting the power requirement for a searchlight-scale carbon arc lamp. The US Navy Model 24-G-20 24-inch searchlight used in WW II was operated at an arc current of 75-80 amperes and an arc voltage of 65 to 70 volts. However, the line voltage was 105-125 volts, so almost half the power was absorbed by the rheostat/ballast (General Electric). That corresponds to a power draw of 7875-10,000 watts. If we assume 80% efficiency in the generator and distribution system again, then we would need as much as 12,500 watts, and thus a steam engine of about 17 hp. That seems doable.
In fact, the Royal Anne, an airship built in Copenhagen and first flying in September 1636, has six steam engines (Evans, “No Ship for Tranquebar Part Two” Grantville Gazette 28), and I suspect that these steam engines correspond to those that Evans proposed for a medium-sized cargo airship in his “Wingless Wonders” (Grantville Gazette 19). Those engines were nine-cylinder, single-acting, “with 300 hp generated when running at full speed (2200 rpm, 400 psi).”
If electricity is unavailable, there is a chemical alternative. Limelights, invented by an ordnance survey officer in 1822, were first used theatrically in 1836. They relied on the reaction of oxygen and hydrogen gases with quicklime (calcium oxide). That reaction is potentially explosive, and the safest format is one in which the two gas jets meet at an angle where the lime cylinder is located (Encyclopaedic Dictionary of Photography 303).
Limelights were used by the Union Navy during its bombardment of Charleston in September, 1863 and to spot blockade runners in early 1865 (IATSE, KCWB, Navy 1). Drummond used the lime light (supposedly equivalent to “about 265 flames of an ordinary Argand lamp used with the best Sperm Whale oil”) in conjunction with a 21-inch parabolic reflector for geodetic purposes; the combination produced about 92,000 candlepower. While he urged its use in lighthouses, the American Lighthouse Board reported in 1868: “The Lime light required much labor, there was danger associated with the production of the gases used, it required expensive apparatus, and the liability of the lime to become deranged far outweighed any advantages in the way of superior illumination, which could be derived from it.” (USLS).
Some sort of chemical-based searchlight was still available for military use in the early twentieth century, but its useful range was something like one-eighth that of the 36-inch electric search light (Ordnance, 37).
The navy would likely rather use carbon arc searchlights, on both safety and performance grounds.
Light Concentration. Note that the “candlepower” (light intensity in the direction of the target) of a light increases if its light is more tightly focused, even though the total light output is constant. A searchlight may have millions of candlepower in its beam. Light may be concentrated by mirrors, lenses, or combinations of the two.
Reflectors. The earliest documented use of a polished metal reflector to concentrate candlelight was in 1532, at the lighthouse of Gollenberg. In 1669, Braun used a cast steel reflector with an oil lamp at the lighthouse of Landsort, Sweden (USLS). American Civil War searchlights used crude mirrors made of an unspecified metal that absorbed one-third to one-half of the incident light (Nerz 713).
Reflector shape. The ideal shape (figure) for a reflector is parabolic; if the light source is at the focal point, then all of the reflected rays will be parallel to the optical axis of the reflector. There were occasional experiments with spherical reflectors at lighthouses, since the spherical shape was easier to achieve. These proved to provide little concentration (USLHS).
For the techniques of grinding a mirror to a parabolic shape, see Cooper, “Seeing the Heavens” (Grantville Gazette 14),
Reflective Material. The ideal reflective material would be highly reflective across the visible light spectrum, easily formed into the parabolic shape, resistant to corrosion (tarnishing), easily cleaned and polished, low in density, and inexpensive. Most modern mirrors are composites—typically a metal coating on a glass or plastic substrate.
For metals, the reflectivities at 400 (blue) and 700 nm (red) are as follows: gold* (39%, 96%), copper* (51%, 95%), silver* (87%, 97%), aluminum (92%, 91%), iron* (48%, 54%), tungsten (46%, 52%), tin* (75%, 83%), chromium (69%, 64%), and rhodium (76%, 81%). Only the asterisked metals are known to European metalworkers at the eve of the RoF. Plainly, silver and aluminum are the best from a purely optical standpoint.
Silver of course is expensive and so there is some advantage to combining the high reflectivity of a silver coating with a lower-cost metal. A silvered copper parabolic reflector was fitted to the La Heve lighthouse in 1781 (Marriott 25). Robert Stevenson combined an Argand lamp with a silver-clad copper parabolic reflector and, installed at the Bell Rock lighthouse in 1811, it produced 2500 candlepower (USLHS).
Silver, however, is subject to tarnishing as a result of hydrogen sulfide in the atmosphere (or in perspiration if the mirror surface is touched). The resulting silver sulfide is black. The tarnishing is more rapid if the air is humid.
Costs could be reduced further by use of speculum metal (45% tin, 55% copper). Its reflectivities are 63% at 0.45 and 75% at 0.65 (Tolansky). Unfortunately, it, too, tarnishes, and it is also somewhat brittle.
The first telescope with a parabolic mirror was built by Hadley in 1721. It was a six-inch diameter piece of speculum metal. The Royal Society praised his achievement, but expressed the hope that someone would either figure out how to keep the metal from tarnishing or how to make a silvered glass mirror (Pendergrast 161). This proved to be a difficult proposition, and speculum continued to be used well into the nineteenth century.
When a metal mirror needed to be cleaned it also had to be repolished and often refigured. The Rosse telescope (1845), the largest in the world until 1917, had two six-foot speculum mirrors, one would be in use while the other was being refigured (Pendergrast 176-80).
For those for whom cost was an issue, Fitzmaurice invented platinum-glazed porcelain reflectors. They cost one-quarter of the equivalent silvered metal reflector but were inferior in performance. They were used at Sunderland Lighthouse (1860).
Various methods of “silvering” glass were discussed in Cooper, “In Vitro Veritas: Glassmaking After The Ring Of Fire” (Grantville Gazette 5).
Down-time glass mirrors weren’t actually silvered; rather a tin-mercury amalgam was applied to the rear surface of the glass. After 1732, James Short tried and failed to use this method to make a paraboloid mirror; he switched to speculum metal (Pendergrast 161). In 1788, Rogers made lighthouse reflectors of “silvered” glass, but they proved to be too fragile USLHS).
Advances in the arts of silvering glass and of grinding glass to paraboloidal shape made possible the silvered glass paraboloidal mirror.
In 1835, von Liebig discovered how to deposit pure silver on glass by chemically reducing (with sugar) a boiling silver nitrate solution. Drayton patented several cold processes in the 1840s but the mirrors so manufactured were unsatisfactory (e.g., developed brownish red spots after a few weeks—”measles!”) (Chattaway).
Liebig came to the rescue in 1856 with the first truly satisfactory method, which used caustic soda and ammonia to accelerate the reduction. In 1856, Steinheil used it to silver a four-inch diameter telescope mirror (King 262). Foucault likewise made a silvered glass receptor in 1857, but used one of Drayton’s silvering methods (Chattaway). There were further advances in the silvering art that came later (Common). One such was Cimeg’s (1861), with Rochelle salt as the reducing agent. EB11/Mirrors describes the Brashear method (1884) in great detail.
In 1858, Foucault devised the knife-edge test, which could be used to determine how much a glass surface departed from spherical. Hence, you could make an accurate paraboloid surface by an iterative hand grind-and-check process. The same year, he made a 40-centimeter silvered glass paraboloid telescope mirror. The method was perfected by Draper in the 1870s, who preferred the Cimeg silvering process (Lemaitre 20).
Nonetheless, governments contented themselves in the 1880s with inferior catadioptric reflectors of the Mangin type (see below) for military searchlights (Burstyn). In 1885, Schuckert “invented a machine that could accurately grind glass into a parabolic” curve (USLHS) and quickly put this to work in making searchlight mirrors. These Schuckert searchlights were used in 1887-8 in the Italian campaign in Ethiopia (Rey 97), and a Schuckert searchlight was exhibited at the 1893 Chicago World’s Fair. Schuckert mirrors of 30-inch diameter were used to make forty million-candlepower searchlights for the Heligoland lighthouse in 1902.
Articles in the electrical and military literature credit him with being the first to make “paraboloid glass mirrors with a sufficient degree of accuracy for searchlight work” (Murdock 359). Were they simply ignorant of the existence of telescope mirrors of that type? Or was the hand-grinding done by telescope makers prohibitively expensive for military and lighthouse use?
In 1909, the mirror alone for Lowell’s 42-inch reflector cost $10,800 ($209,200 is the 2001 equivalent) (Cameron 117); a Model-T Ford in 1910 cost $950 (135). (It is conceivable that the high price was necessitated by the degree of accuracy demanded for astronomical work, rather than the hand-grinding.)
What about tarnishing? On a telescope, the silvering must be applied to the front surface, to avoid ghost reflections from the glass. Hence, the silver is exposed to the atmosphere. It does tarnish, but it was discovered that the old coating could be removed and a new one applied without loss of the parabolic figure.
On a searchlight reflector, the silvering can be applied to the rear surface, where it is more protected from the atmosphere. However it will still deteriorate with time.
With large carbon arc searchlights, the heat generated may be such that one cannot use ordinary glass, but rather thermal shock-resistant borosilicate glass (Pyrex).
In NTL 1636, aluminum may be available, but only in experimental quantities. For the necessary raw materials and processes, see Cooper, “Aluminum: Will O’ the Wisp” (Grantville Gazette 8).
Aluminum is highly reflective and only a little denser than glass. Aluminum reacts with oxygen in the atmosphere, but the resulting aluminum oxide is clear and hard, protecting the aluminum from further attack. A mirror was first aluminized in 1932 and an aluminized glass reflector was first used in a telescope in 1935. Aluminization of glass requires a high vacuum, but the film is more durable (Yoder 62). Mirrors may also be made entirely of cast aluminum (264).
For the sake of completeness, I note that other metals have also been used as reflective coatings. Rhodium plating has been used for dental mirrors and chromium for the rear view mirrors in cars.
A continuing concern with silvered (or aluminized) glass searchlight mirrors was vulnerability to breakage—the enemy had a tendency to shoot at searchlights. Two types of coated metal mirrors were tested in World War I; one had its coating destroyed after a few hours exposure to the carbon arc, and the other was of inferior illuminating power to a silvered glass mirror (Baird 10-11).
In World War II, we had 60-inch, 800,000 candela carbon arc searchlights that used a rhodium-plated parabolic mirror (Wikipedia/Searchlight).
Segmented reflectors. Hutchinson built faceted reflectors in 1763-77. Some of his designs were tin plates soldered together, but the largest, twelve feet in diameter, was of wood with pieces of mirror glass (clear glass coated with a tin-silver amalgam) attached to approximate the parabolic shape. It was coupled to an oil lamp and reportedly could be seen ten miles away.
Another glass-faceted reflector was produced by Walker (18-inch parabolic reflector for the Old Hunstanton Lighthouse, 1776). The facets were set in a parabolic plaster shell in a metal frame. Reportedly, its beam of 1000 candlepower was two-thirds the intensity of a one-piece parabolic reflector of the same diameter. Thomas Smith similarly built an 18-inch parabolic reflector with 350 pieces of mirror glass. Used with a lamp having four rope wicks, the combination produced 1000 candlepower at the Kinnaird Head lighthouse in 1787.
A modern twist on this old idea would be to use spin-casting to create the shell. In essence, when a liquid is spun, its surface takes on a concave paraboloid shape because of the combination of the gravitational and centripetal forces acting upon it. All we need, then, is a substance that will harden into that shape. Appleyard reports that both gelatin and melted wax work. De Paula used plaster. The resulting figures are adequate for solar heating, and hence also for searchlights.
Spin-casting can be used in place of grinding to create glass paraboloid mirror blanks for telescopes, but you need a rotating furnace, and the molten glass must be cooled slowly (over several months). For telescope use, there is further milling and polishing to make the surface as accurate as possible (Mirror Lab). We don’t need this!
Lens. Big telescopes use mirrors rather than lenses of the same diameter because the latter are much more expensive. However, Fresnel invented a lens composed of separate concentric annular sections, whose surfaces approximate that of a simple lens of the same focal length. Since it is only using the part of the glass that contributes to the proper refraction of the light, it is much lighter and less costly than a simple lens.
The more sections there are, the less degradation in performance relative to a one-piece lens, but the greater the cost. The sections may have curved (better concentration) or flat (cheaper) surfaces. A Fresnel lens was first used in a light house in 1823 (Wikipedia/Fresnel Lens). The largest (“hyper-radial”) had a height of 148 inches and weighed 18,485 pounds. For a ship’s searchlight we would probably use one of “third order” (62 inch height, 1984 pounds) or smaller (USLHS).
Mirror-Lens Combinations. Robert Stevenson invented (1849) the holophotal reflector. This combined a central spherical reflector, a peripheral parabolic reflector and a Fresnel lens, and the point was to capture essentially all of the light from the source (USLHS).
Mangin reflectors were invented in 1876 for use with the carbon arc (Navy 1). This was a lens having two concave surfaces of different radii, the front surface having the shorter radius, and the back surface having a reflective coating (thus constituting a spherical mirror). The radii were chosen so the spherical aberration produced by the lens was exactly opposite to that produced by the reflective coating.
The Mangin reflector had the disadvantage that it had a longer focal length and therefore a smaller effective angle than a parabolic mirror of the same diameter; if the diameter were 60 centimeters, the angles would be 83o and 123o respectively, and as a result the parabolic reflector would gather 2.11 times as much light (Nerz 715) .
Weight. Can a NTL 1630s ship accommodate the weight of a searchlight and its power source? Insofar as the steam engine (including boiler) is concerned, I discussed the issue a bit in “Airship Propulsion: Part Three: Steaming Along” (Grantville Gazette 43). The big uncertainty is the weight of the condenser. For use on shipboard, bringing down the weight of the condenser is less critical, so let’s just say six pounds per horsepower—that’s 102 pounds for the 17 hp steam engine postulated above.
I don’t have figures for the weight of a 24-inch searchlight, but for a sixty-inch one (delivering 800 million candlepower!), with the six-cylinder gasoline engine, 16.7 kW generator, carbon arc, metal mirror, protective glass, and aiming apparatus all mounted on a small four-wheeled trailer, the combined weight was six thousand pounds. (Fort Macarthur). That may seem like a lot, but it was not unusual for a mid-nineteenth century naval gun to weigh 150-200 times the weight of its shot (Ward 30), which would make the 60-inch searchlight equivalent to a 30- to 40-pounder. (And in the late seventeenth century guns were heavier, 175-250 times shot weight (Glete 516).) If weight scales with beam area, then the 24-inch would weigh only 1,000 pounds, and a 12-incher would weigh 250 pounds.
Nighttime Light Signals
A ship might need to communicate with a friendly ship or with the shore. Daytime signaling with mirrors or smoke is ancient, but those aren’t useful at night. Until radio communications become readily available, light signals may be useful. Bear in mind that light communications may be more difficult to intercept than radio ones once the enemy has radio receivers.
It is worth noting that it takes “5 to 20 times as much light to distinguish the color of a light than to simply distinguish” its presence or absence (Lewis 34).
Pyrotechnics may be handheld (like sparklers), attached to a scaffolding, or fired into the air by rockets, mortars, or signal pistols. The last of these was found to be particularly convenient. Pyrotechnics provide an intense but brief illumination.
The first firework colors were ambers and off-whites (Plimpton 161), and it is possible that those were the only ones available in 1630s Europe Babington’s Pyrotechnia (1635), chapter VIII claims to be able to make “stars” of “a blue color with red”, but the ingredient list is suspect: saltpeter, sulfur vive, aqua vitae, and oyl of spike. More plausibly, Wright’s Notes on Gunnery (1563) and Appier-Hanzelet’s La Pyrotechnie (1630) proposed adding verdigris (copper sulfate) to obtain green, but this green was deemed unsatisfactory by later pyrotechnicians (Werrett 160-2, 230, 281 n. 117).
My expectation is that shortly after the Ring of Fire there would have been research in Grantville as to how to attain red and blue (for the Fourth of July, of course!).
For red, one may use calcium, from the calcium carbonate of chalk, eggshells, or seashells. But this would be rather orange-y, and would be replaced as soon as possible with strontium salts. Strontianite was available from lead mines in Braunsdorf near Freiburg in Saxony, and from the marls of Munster and Hamm in Westphalia (EB11/Strontianite).
Blue could come from copper salts, several of which had long been known to the alchemists. The “resin of copper,” copper chloride, was first synthesized in the old timeline by Robert Boyle in 1664; it was easy enough to make from copper and corrosive sublimate, as Boyle had demonstrated, or by other methods.
By the mid-nineteenth century, the preferred green was from barium salt. Barite (barium sulfate) can be found in mines in the Black Forest and in Saxony and is reasonably likely to show up in a “canned” mineral collection sold to the high school for use in geology classes.
All of these colorants are disclosed in EB11/Fireworks.
Pyrotechnic signal codes. A two-color pyrotechnic signal system was conceived by Benjamin Coston in the 1840s, and a three-color one was developed and patented in his name (USP 23,356, 1859) by his widow, Martha Coston. According to this patent, the numerals 0 to 9 were represented by red, white and blue flares, either individually (for “1” to “3”) or a sequence of two (e.g., white then red for “4”) or three different colors (white then red then blue for “9”). The signals were fired from a signal gun. There were three different sizes of paper boxes that could be set off (either by hand percussion or by the percussion cap of a signal pistol), the larger sizes contained two or three different pyrotechnic compositions that would be burnt through in succession, corresponding to the key for that numeral. This was intended of course for use with a signal code book in which words or phrases were represented by numerical codes.
It was not possible to achieve a bright blue, and in American Civil War implementation, green was used instead. Short white, red and green represented 1-3; long red, 4; long green, 5; white-red, 6 green-red, 7; white-green, 8; red-green, 9; and green-red-white, 0. There was also a “P” (white-red-white) meaning “preparing to send a signal” and an “A” (red-white-red) to acknowledge the preparatory signal.
In 1878, the US Navy began using the Very code, which used a pattern of four bursts, each of which could be red or green, to encode numbers. Despite being a binary code, it did not correspond to Morse code in its original implementation (Wrixon 430).
Signal lamps. In 1617, Raleigh used a fire signal aboard his flagship to send commands to the other ships in his squadron. Given the general availability of lanterns on ships, I would imagine that he was not the only naval commander to do this (Wrixon 417).
A kerosene lamp with a focusing lens (Begbie lamp) came into use in the 1880s and was used until World War I (QSCVC). Subsequently, signal lamps were of the handheld incandescent (Aldis) or pedestal-mounted carbon arc type. Of course, signal lamps would require less power than searchlights of the same effective range.
In the NTL Baltic War, all of Simpson ships had signal searchlights converted from mining truck headlamps (Flint, 1634: The Baltic War, chapter 37).
It may be of interest to note that over the horizon communication is possible if there are cloud bases that can be illuminated.
Also, passing into the weird tech department, it is possible to transmit speech rather than Morse code at short ranges, with the appropriate receiver. Photophony was demonstrated by Simon in 1901 over a 0.72 mile distance using a Schuckert 90-centimeter searchlight as the transmitter and a 30-inch parabolic mirror with a selenium cell at the focal point as the receiver. The major limitation on photophony range was the combination of the divergence of the beam and the intensity of the light source. With a three degree divergence, a 30-centimeter beam would spread out to 150 meters at a range of three kilometers, and the intensity is reduced to four-millionths of the source (Burns 202-4).
Selenium is available according to canon; in October 1633, a radio with a selenium photo-resistor amplifier is being installed in a village, see Huff and Goodlett, “Credit Where It’s Due” (Grantville Gazette 36). Selenium is usually obtained as a byproduct of refining copper, being associated with copper sulfide ores (chalcocite, chalcopyrite). There is reference to electrorefining in Carroll and Wild, “The Undergraduate, Episode Two” (Grantville Gazette 50).
Signal lamp codes. In 1616, Franz Kessler proposed a binary code for use with a shuttered lantern for encoding letters of the alphabet and thereby sending messages (Ibid.). In 1862-3, Colomb used the combination of limelight and a shutter to send signals by Morse code (Sterling 209).
An alternative approach, used by Preble in 1803, relied on the spatial arrangement of three or four lanterns to encode numbers and a few special signals (Wrixon 419).
Colored light systems were proposed, too. In the 1850s, Ward proposed signals using combinations of red, white and no light (422). The Berg system used red, white, and green.
In 1891, the US Navy adopted the Ardois system. It used a cluster of four double lamps read top to bottom or sender’s right to left; within the pair, the upper light was red (Morse dot) and the lower light white (Morse dash); the light sources were 32-watt incandescents (424).
Combination Signals. The Royal Navy’s Night Signal Book for the Ships of War (1799) used a combination of lanterns, rockets, and “blank” cannon fires to encode numbers, which in turn had meanings specified in the code book (Wrixon 418).
Sometimes the Coston flares were combined with rockets. For example, the force blockading Charleston in 1864 used a rocket followed by Coston No. 0 for “blockade runner going out.”
Combinations signals were made easier to interpret by Greene, who advocated timing the intervals between signals, making it easier to figure out when one signal sequence ended and the next began.
Warships with sufficient electric power are likely to get equipped with a carbon arc searchlight. While it should be possible to prepare a silvered glass mirror by the Liebig process, my guess is that the first NTL searchlight mirrors will not be one-piece mirrors, but rather faceted mirrors in order to improve durability.
I would also expect them to use star shells, Until magnesium is available, these will probably use down-time “white star” compositions. However, I expect that some inventor will figure out how to add the parachute.