Candle clock

A candle clock is a thin candle with consistently spaced markings (usually with numbers), that when burned, indicate the passage of periods of time. While no longer used today, candle clocks provided an effective way to tell time indoors, at night, or on a cloudy day. A candle clock could be easily transformed into a timer by sticking a heavy nail into the candle at the mark indicating the desired interval. When the wax surrounding the nail melts, the nail clatters onto a plate below.

It is unknown where and when candle clocks were first used. The earliest reference to their use occurs in a Chinese poem by You Jiangu (520 CE). Here, the graduated candle supplied a means of determining time at night. Similar candles were used in Japan until the early 10th century.

You Jiangu's device consisted of six candles made from 72 pennyweights of wax, each being 12 inches high, of uniform thickness, and divided into 12 sections each of one inch. Each candle burned away completely in four hours, making each marking 20 minutes. The candles were placed for protection inside cases made of a wooden frame with transparent horn panels in the sides. Similar methods of measuring time were used in medieval churches and earlier, famously by King Alfred the Great of England, first by counting the number of candles of a specific size burnt, and later by use of a graduated candle.

Al-Jazari

The most sophisticated candle clocks known to date, however, were those of Al-Jazari in 1206.^[1] It included a dial to display the time and, for the first time, employed a bayonet fitting, a fastening mechanism still used in modern times.^[2] Donald Routledge Hill described one of al-Jazari's candle clocks as follows:

The candle, whose rate of burning was known, bore against the underside of the cap, and its wick passed through the hole. Wax collected in the indentation and could be removed periodically so that it did not interfere with steady burning. The bottom of the candle rested in a shallow dish that had a ring on its side connected through pulleys to a counterweight. As the candle burned away, the weight pushed it upward at a constant speed. The automata were operated from the dish at the bottom of the candle.^[1]

References

Turner, Anthony J. The Time Museum, Volume I, Time Measuring Instruments; Part 3, Water-clocks, Sand-glasses, Fire-clocks

1. Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", Scientific American, May 1991, pp. 64-9 (cf. Donald Routledge Hill, Mechanical Engineering)
2. Ancient Discoveries, Episode 12: Machines of the East, History Channel, retrieved 2008-09-07

Dust Veil of AD 526 - 6th Century Environmental Disaster in Europe

According to written records and supported by dendrochronology and archaeological evidence, for 12-18 months in AD 526 , a thick, persistent dust veil or dry fog darkened the skies between Europe and Asia Minor. The climatic interruption brought by the thick, bluish fog extended as far east as China, where summer frosts and snow are recorded in historical records; tree ring data from Mongolia and Siberia to Argentina and Chile reflect decreased growing records from 526 and the subsequent decade.

The climatic effects of the dust veil brought decreased temperatures, drought and food shortages throughout the affected regions: in Europe two years later came the Justinian plague. The combination killed perhaps as much as 1/3 of the population of Europe; in China the famine killed perhaps 80% of people in some regions; in Scandinavia the losses may be been as much as 75-90% of the population, as evidenced by the numbers of deserted villages and cemeteries.

Historical Documentation

The rediscovery of the AD 526 event was made during the 1980s by American geoscientists Stothers and Rampino, who searched classical sources for evidence of volcanic eruptions. Among their other findings, they noted several references to environmental disasters around the world .

Contemporary reports identified by Stothers and Rampino included Michael the Syrian, who wrote "the sun became dark and its darkness lasted for one and a half years... Each day it shone for about four hours and still this light was only a feeble shadow...the fruits did not ripen and the wine tasted like sour grapes." John of Ephesos related much the same events. Prokopios living in in Africa and Italy, said "For the sun gave forth its light without brightness, like the moon, during this whole year, and it seemed exceedingly like the sun in eclipse, for the beams it shed were not clear nor such as it is accustomed to shed."

An anonymous Syriac chronicler wrote "...the sun began to be darkened by day and the moon by night, while ocean was tumultuous with spray, from the 24th of March in this year till the 24th of June in the following year..." and the following winter in Mesopotamia was so bad that "from the large and unwonted quantity of snow the birds perished."

Cassiodorus, praetorian prefect of Italy at the time, wrote "so we have had a winter without storms, spring without mildness, summer without heat". John Lydos, in On Portents, writing from Constantinople, said: "If the sun becomes dim because the air is dense from rising moisture--as happened in AD 526 for nearly a whole year...so that produce was destroyed because of the bad time--it predicts heavy trouble in Europe."

And in China, reports indicate that the star of Canopus could not be seen in as usual in the spring and fall equinoxes of 526 AD were marked by summer snows and frosts, drought and severe famine. In some parts of China, the weather was so severe that 70-80% of the people starved to death.

Physical Evidence

Tree rings show that 526 and the following ten years shows a period of slow growth for Scandinavian pines, European oaks and even several North American species including bristlecone pine and foxtail; similar patterns of ring size decrease are seen in trees in Mongolia and northern Siberia.

But there seems to be something of a regional variation in the worst of the effects. 526 was a bad growing season in many parts of the world, but more generally, it was a part of a decade-long downturn in climate for the northern hemisphere, separate from the worst seasons by 3-7 years. For most reports in Europe and Eurasia, there is a drop in 526,  followed by a more serious plunge lasting perhaps as late as 550. In most cases the worst year for tree ring growth is 540; in Siberia 543, southern Chile 540, Argentina 540-548.

AD 526 and the Viking Diaspora

Archaeological evidence described by Gräslund and Price (2012) shows that Scandinavia might have experienced the worst troubles. Almost 75% of villages were abandoned in parts of Sweden, and areas of southern Norway show a decrease in formal burials up to 90-95%.

Scandinavian narratives recount possible events that might be referring to 526.Snorri Sturluson's Edda includes a reference to Fimbulwinter, the "great" or "mighty" winter that serves as a forewarning of Ragnarök, the destruction of the world and all of its inhabitants. "First of all that a winter will come called Fimbulwinter. Then snow will drift from all directions. There will then be great frosts and keen winds. The sun will do no good. There will be three of these winters together and no summer between."

Gräslund and Price speculate that the social unrest and sharp agrarian decline and demographic disaster in Scandinavian may have been the catalyst for the Viking diaspora.

Possible Causes

Scholars are divided concerning what caused the dust veil: a violent volcanic eruption, a cometary impact, even a near miss by a large comet could have created a dust cloud made up of dust particles, smoke from fires and (if a volcanic eruption) sulfuric acid droplets such as that described. Such a cloud would reflect and/or absorb light, increasing the earth's albedo and measurably decreasing the temperature.

Sources:

Source Of Climatic Effect

Hydroelectric Power

Moving water is a powerful entity responsible for lighting entire cities, even countries. Thousands of years ago the Greeks used water wheels, which picked up water in buckets around a wheel. The water's weight caused the wheel to turn, converting kinetic energy into mechanical energy for grinding grain and pumping water. In the 1800s the water wheel was often used to power machines such as timber-cutting saws in European and American factories. More importantly, people realized that the force of water falling from a height would turn a turbine connected to a generator to produce electricity. Niagara Falls , a natural waterfall, powered the first hydroelectric plant in 1879.

"By the 1940s, the best sites for large dams had been developed." But like most other renewable sources of energy, hydropower could not compete with inexpensive fossil fuels at the time. "It wasn't until the price of oil skyrocketed in the 1970s that people became interested in hydropower again." Today one-fifth of global electricity is generated by falling water.Man-made waterfalls dams were constructed throughout the 1900s in order to maximize this source of energy. Aside from a plant for electricity production, a hydropower facility consists of a water reservoir enclosed by a dam whose gates can open or close depending on how much water is needed to produce a particular amount of electricity. Once electricity is produced it is transported along huge transmission lines to an electric utility company.

"Over the past 100 years, the United States has led the world in dam building. Secretary of the Interior Bruce Babbitt recently observed that, 'on average, we have constructed one dam every day since the signing of the Declaration of Independence.'"Of the 75,187 dams in the US , less than 3% are used to produce 10-12% of the nation's electricity. With over 2,000 facilities, the US is the second largest producer of hydropower worldwide, behind Canada . The dams that do not produce electricity are used for irrigation or flood control. Many people believe these pre-existing sites could contribute to the country's power supply in a cost-effective manner if hydroelectric facilities were constructed.

There are several favorable features of hydropower. Anywhere rain falls, there will be rivers. If a particular section of river has the right terrain to form a reservoir, it may be suitable for dam construction. No fossil fuels are required to produce the electricity, and the earth's hydrologic cycle naturally replenishes the "fuel" supply. Therefore no pollution is released into the atmosphere and no waste that requires special containment is produced. Since "water is a naturally recurring domestic product and is not subject to the whims of foreign suppliers," there is no worry of unstable prices, transportation issues, production strikes, or other national security issues.

Hydropower is very convenient because it can respond quickly to fluctuations in demand. A dam's gates can be opened or closed on command, depending on daily use or gradual economic growth in the community. The production of hydroelectricity is often slowed in the nighttime when people use less energy. When a facility is functioning, no water is wasted or released in an altered state; it simply returns unharmed to continue the hydrologic cycle. The reservoir of water resulting from dam construction, which is essentially stored energy, can support fisheries and preserves, and provide various forms of water-based recreation for locals and tourists. Land owned by the hydroelectric company is often open to the public for hiking, hunting, and skiing. Therefore, "hydropower reservoirs contribute to local economies. A study of one medium-sized hydropower project in Wisconsin showed that the recreational value to residents and visitors exceeded $6.5 million annually." Not to mention the economic stimulation provided by employment.

Hydroelectric power is also very efficient and inexpensive. "Modern hydro turbines can convert as much as 90% of the available energy into electricity. The best fossil fuel plants are only about 50% efficient. In the US , hydropower is produced for an average of 0.7 cents per kilowatt-hour (kWh). This is about one-third the cost of using fossil fuel or nuclear and one-sixth the cost of using natural gas," as long as the costs for removing the dam and the silt it traps are not included. Efficiency could be further increased by refurbishing hydroelectric equipment. An improvement of only 1% would supply electricity to an additional 300,000 households.

Hydropower has become "the leading source of renewable energy. It provides more than 97% of all electricity generated by renewable sources worldwide. Other sources including solar, geothermal, wind, and biomass account for less than 3% of renewable electricity production." In the US , 81% of the electricity produced by renewable sources comes from hydropower. "Worldwide, about 20% of all electricity is generated by hydropower." Some regions depend on it more than others. For example, 75% of the electricity produced in New Zealand and over 99% of the electricity produced in Norway come from hydropower. For information on making a hydro power system refer our page "Producing Hydro"

The use of hydropower "prevents the burning of 22 billion gallons of oil or 120 million tons of coal each year." In other words, "the carbon emissions avoided by the nation's hydroelectric industry are the equivalent of an additional 67 million passenger cars on the road 50 percent more than there are currently." The advantages of hydropower are therefore convincing, but there are some serious drawbacks that are causing people to reconsider its overall benefit.

Since the most feasible sites for dams are in hilly or mountainous areas, the faults that often created the topography pose a great danger to the dams and therefore the land below them for thousands of years after they have become useless for generating power. In fact, dam failures do occur regularly due to these terrain conditions, and the effects are devastating.

When a new dam's reservoir floods the countryside, people who live in the area have to move and relinquish their former lifestyles in order to make way for the project. This is very stressful and often controversial, especially if a community has maintained a particular way of life on the same land for generations. Such is the case in Chile, where the indigenous Pehuenche "are currently fighting construction of the 570MW, US $500,000,000 Ralco Dam on the Biobo River Eight families continue to refuse to negotiate land exchanges with Endesa [the utility company], and wish to remain on their lands." If the project succeeds, a 13-square-mile reservoir would flood the land and force 600 people out of their homes, 400 of whom are Pehuenche "whose ancestral home is the upper Biobo." A total of five dams have been planned, which "would force the relocation of 1,000 Pehuenches, 20% of the survivors of this ancient culture."

The construction of a dam not only affects the people nearby, it can severely alter a river's natural functions. According to American Rivers, a conservation organization, "by diverting water for power, dams remove water needed for healthy in-stream ecosystems. Stretches below dams are often completely de-watered." This may not seem like a significant problem until animal species are studied. Birds that have migrated to a specific riparian environment for generations no longer have enough insects on which to prey when the water level drops. If they have few migration alternatives, that could mean the endangerment of species that once flourished. Fish species such as salmon "depend on steady flows to flush them down river early in their life and guide them upstream years later to spawn. Stagnant reservoir pools disorient migrating fish and significantly increase the duration of their migration." Native populations of fish may decrease or disappear altogether due to temperature changes caused by dams. Slower water flow means warmer temperatures, and bottom-release of cold water means cooler temperatures. Several of hydropower's disadvantages focus on fish. It is easy to forget how important fish and other aquatic life are, some of which reside at the bottom of the food chain.

The environmental changes caused by hydroelectric projects may be obvious to the local biologist, but elude the average person. Most people will more readily notice a smoggy haze developing in an area where a coal plant is operating than a smaller population of a particular bird species where a hydropower facility functions. Such oversights lead people to believe that nothing is wrong.

Hydroelectric companies and organizations often emphasize their "clean" manufacture of electricity and neglect to mention the long-term environmental hazards. "Dams hold back silt, debris, and nutrients." Silt collects behind the dam on the river bottom, accumulating heavy metals and other pollutants. Eventually this renders the dam inoperable, leaving the mess for future generations, who will either have to remove the collected debris or live with a potentially catastrophic mudflow poised to inundate the area below the dam.

There is also a debate between preserving rivers for their aesthetic value versus meeting the energy needs of thousands of people. The latter has prevailed. Today "there are 600,000 river miles impounded behind dams. In contrast, only 10,000 river miles (not even half of 1%) are permanently protected under the National Wild and Scenic Rivers System." The only undammed river in the US that is longer than 600 miles is the Yellowstone .

Hydropower may be better on the environment than fossil-fuel sources, but its future is so uncertain that we may need to focus on other alternatives. According to the National Hydropower Association, "an increasing array of statutes, regulations, agency policies and court decisions have made the hydroelectric licensing process costly, arbitrary and time-consuming. A typical hydropower project takes 8 to 10 years to find its way through the licensing process. By comparison, a natural gas fired plant, which emits significant carbon dioxide (CO 2 ) gases, can typically be sited and licensed in 18 months. Given this uncertain climate, few investors are willing to risk their capital on new hydropower development. Furthermore, some project owners and operators contemplate abandonment of their projects rather than proceeding with relicensing."

Relicensing is a complex process in which private dams are re-evaluated every 30 to 50 years. The Federal Energy Regulatory Committee "considers anew whether it is appropriate to commit the public's river resources for private power generation FERC is now required, when deciding whether to issue a license, to consider not only the power generation potential of a river, but also to give equal consideration to energy conservation, protection of fish and wildlife, protection of recreational opportunities, and preservation of other aspects of environmental quality." Relicensing was infrequent until 1993, when hundreds of licenses began to expire. "The Hydropower Reform Coalition formed in 1992 to take advantage of this once-in-a-lifetime opportunity to restore river ecosystems through the relicensing process." To the Coalition's dismay, a new bill is being considered called the Hydroelectric Licensing Process Improvement Act, which if passed, "would limit the abilities of federal agencies to protect natural resources," making relicensing easier for dam operators.

Some people favor dam removal so that healthy rivers and riverside communities can be restored, but American Rivers reports that most of the larger dams in the US "are not likely candidates for removal." In that case it may be wasteful not to use them to their full potential as long as they are still sturdy. A hydropower assessment conducted by the US Department of Energy found that 4,087 sites could be developed without constructing a new dam. "The assessment consider[ed] such values as wild/scenic protection, threatened or endangered species, cultural values and other non-power issues. If all of this potential were to be developed 22.7 million metric tons of carbon could be avoided." But this savings in carbon emissions pales when compared to the tonnage of silt and other material that must be handled if the river is to be restored to a freely-flowing state. All rivers will eventually silt up the dam. At this point future generations will have the choice to either keep the useless dam or remove it. Keeping the poorly consolidated silt and mud behind the dam is potentially dangerous. Removal costs will often exceed the value of power produced over the dam's lifetime.

Unlike other renewables such as wind and solar power that receive more praise than criticism, hydropower is a highly controversial issue. While it does have many merits, it too is like so many other sources of energy if we ignore the critics' warnings, we may not realize its full impact on our natural resources until it is too late.

Sources:

Norway is Europe's largest oil producer, the world's third-largest natural gas exporter, and an important supplier of both oil and natural gas to other European countries