In botany, a bulb is structurally a short stem with fleshy leaves or leaf bases[1] that function as food storage organs during dormancy. (In gardening, plants with other kinds of storage organ are also called "ornamental bulbous plants" or just "bulbs".)

A bulb's leaf bases, also known as scales, generally do not support leaves, but contain food reserves to enable the plant to survive adverse weather conditions. At the center of the bulb is a vegetative growing point or an unexpanded flowering shoot. The base is formed by a reduced stem, and plant growth occurs from this basal plate. Roots emerge from the underside of the base, and new stems and leaves from the upper side. Tunicate bulbs have dry, membranous outer scales that protect the continuous lamina of fleshy scales.[2] Species in the genera Allium, Hippeastrum, Narcissus, and Tulipa all have tunicate bulbs. Non-tunicate bulbs, such as Lilium and Fritillaria species, lack the protective tunic and have looser scales.[3]

Stem morphology type bulb
Longitudinal section through bulb
Red onion cross section 04
Cross section of onion bulb

The technical term geophyte encompasses plants that form underground storage organs, including bulbs as well as tubers and corms. Some epiphytic orchids (family Orchidaceae) form above-ground storage organs called pseudobulbs, that superficially resemble bulbs.

Nearly all plants that form true bulbs are monocotyledons, and include:

Oxalis, in the family Oxalidaceae, is the only dicotyledon genus that produces true bulbs.[4][5]

Bulbous plant species cycle through vegetative and reproductive growth stages; the bulb grows to flowering size during the vegetative stage and the plant flowers during the reproductive stage. Certain environmental conditions are needed to trigger the transition from one stage to the next, such as the shift from a cold winter to spring.[2] Once the flowering period is over, the plant enters a foliage period of about six weeks during which time the plant absorbs nutrients from the soil and energy from the sun for setting flowers for the next year. Bulbs dug up before the foliage period is completed will not bloom the following year but then should flower normally in subsequent years.

After the foliage period is completed, bulbs may be dug up for replanting elsewhere. Any surface moisture should be dried, then the bulbs may be stored up to about 4 months for a fall planting. Storing them much longer than that may cause the bulbs to dry out inside and become nonviable.

Shallot bulbs
Hippeastrum (amaryllis) bulb


A bulbil is a small bulb, and may also be called a bulblet, bulbet, or bulbel.[6]

Small bulbs can develop or propagate a large bulb. If one or several moderate-sized bulbs form to replace the original bulb, they are called renewal bulbs.[6] Increase bulbs are small bulbs that develop either on each of the leaves inside a bulb, or else on the end of small underground stems connected to the original bulb.[6]

Some lilies, such as the tiger lily Lilium lancifolium, form small bulbs, called bulbils, in their leaf axils. Several members of the onion family, Alliaceae, including Allium sativum (garlic), form bulbils in their flower heads, sometimes as the flowers fade, or even instead of the flowers (which is a form of apomixis). The so-called tree onion (Allium × proliferum) forms small onions which are large enough for pickling.

Some ferns, such as the hen-and-chicken fern, produce new plants at the tips of the fronds' pinnae that are sometimes referred to as bulbils.

Lilium lancifolium bulbils

Bulbils form in the leaf axils of Lilium lancifolium


Wild garlic (Allium vineale) bulbils sprouting

Allium fistulosum bulbifera0

"Tree onions" form clusters of small bulbs instead of flowers

Further reading

  • Coccoris, Patricia (2012) The Curious History of the Bulb Vase. Published by Cortex Design. ISBN 978-0956809612


  1. ^ Bell, A.D. 1997. Plant form: an illustrated guide to flowering plant morphology. Oxford University Press, Oxford, U.K.
  2. ^ a b Mishra, S.R. (2005). Plant Reproduction. Discovery Publishing House. pp. 120–125. ISBN 978-81-7141-955-5.
  3. ^ Ellis, Barbara W. (2001). Bulbs. Houghton Mifflin Harcourt. p. 3. ISBN 978-0-618-06890-6.
  4. ^ Hartmann, Hudson Thomas; Dale E. Kester (2002). Hartmann and Kester's Plant Propagation: Principles and Practices (7 ed.). Prentice Hall. p. 561. ISBN 978-0-13-679235-2.
  5. ^ Oberlander, K. C.; Emshwiller, E.; Bellstedt, D.U. & Dreyer, L.L. (2009). "A model of bulb evolution in the eudicot genus Oxalis (Oxalidaceae)". Molecular Phylogenetics & Evolution. 51 (1): 54–63. doi:10.1016/j.ympev.2008.11.022.
  6. ^ a b c Bell, A.D. (1997). Plant form: an illustrated guide to flowering plant morphology. Oxford, U.K.: Oxford University Press.
Bulb Energy

Bulb Energy Ltd., trading as Bulb, is a privately financed energy supply company operating in the United Kingdom, based in London. Bulb began trading in August 2015, buying and selling electricity and gas to supply domestic properties. It is one of over 70 smaller energy companies competing with the "Big Six energy suppliers" which dominate the UK market. Bulb competes on price, offering a single variable tariff. It buys all its electricity and 10% of gas from renewable sources. Attracting venture capital, Bulb currently runs at a financial loss while achieving rapid growth in customers.

As of March 2019 Bulb has over a million customers, representing a 3% domestic market share. It is the largest supplier of renewable energy in the UK, and the eighth largest supplier overall.

Compact fluorescent lamp

A compact fluorescent lamp (CFL), also called compact fluorescent light, energy-saving light, and compact fluorescent tube, is a fluorescent lamp designed to replace an incandescent light bulb; some types fit into light fixtures designed for incandescent bulbs. The lamps use a tube which is curved or folded to fit into the space of an incandescent bulb, and a compact electronic ballast in the base of the lamp.

Compared to general-service incandescent lamps giving the same amount of visible light, CFLs use one-fifth to one-third the electric power, and last eight to fifteen times longer. A CFL has a higher purchase price than an incandescent lamp, but can save over five times its purchase price in electricity costs over the lamp's lifetime. Like all fluorescent lamps, CFLs contain toxic mercury which complicates their disposal. In many countries, governments have banned the disposal of CFLs together with regular garbage. These countries have established special collection systems for CFLs and other hazardous waste.

The principle of operation remains the same as in other fluorescent lighting: electrons that are bound to mercury atoms are excited to states where they will radiate ultraviolet light as they return to a lower energy level; this emitted ultraviolet light is converted into visible light as it strikes the fluorescent coating (as well as into heat when absorbed by other materials such as glass).

CFLs radiate a spectral power distribution that is different from that of incandescent lamps. Improved phosphor formulations have improved the perceived color of the light emitted by CFLs, such that some sources rate the best "soft white" CFLs as subjectively similar in color to standard incandescent lamps.White LED lamps now compete with CFLs for high-efficiency lighting, and General Electric is stopping production of domestic CFL lamps in favour of LEDs.

Electric light

An electric light is a device that produces visible light from electric current. It is the most common form of artificial lighting and is essential to modern society, providing interior lighting for buildings and exterior light for evening and nighttime activities. In technical usage, a replaceable component that produces light from electricity is called a lamp. Lamps are commonly called light bulbs; for example, the incandescent light bulb. Lamps usually have a base made of ceramic, metal, glass or plastic, which secures the lamp in the socket of a light fixture. The electrical connection to the socket may be made with a screw-thread base, two metal pins, two metal caps or a bayonet cap.

The three main categories of electric lights are incandescent lamps, which produce light by a filament heated white-hot by electric current, gas-discharge lamps, which produce light by means of an electric arc through a gas, and LED lamps, which produce light by a flow of electrons across a band gap in a semiconductor.

Before electric lighting became common in the early 20th century, people used candles, gas lights, oil lamps, and fires. English chemist Humphry Davy developed the first incandescent light in 1802, followed by the first practical electric arc light in 1806. By the 1870s, Davy's arc lamp had been successfully commercialized, and was used to light many public spaces. Efforts by Swan and Edison

led to commercial incandescent light bulbs becoming widely available in the 1880s, and by the early twentieth century these had completely replaced arc lamps.The energy efficiency of electric lighting has increased radically since the first demonstration of arc lamps and the incandescent light bulb of the 19th century. Modern electric light sources come in a profusion of types and sizes adapted to many applications. Most modern electric lighting is powered by centrally generated electric power, but lighting may also be powered by mobile or standby electric generators or battery systems. Battery-powered light is often reserved for when and where stationary lights fail, often in the form of flashlights, electric lanterns, and in vehicles.

Fibrous tunic of eyeball

The sclera and cornea form the fibrous tunic of the bulb of the eye; the sclera is opaque, and constitutes the posterior five-sixths of the tunic; the cornea is transparent, and forms the anterior sixth.

The term "corneosclera" is also used to describe the sclera and cornea together.

Flash (photography)

A flash is a device used in photography producing a flash of artificial light (typically 1/1000 to 1/200 of a second) at a color temperature of about 5500 K to help illuminate a scene. A major purpose of a flash is to illuminate a dark scene. Other uses are capturing quickly moving objects or changing the quality of light. Flash refers either to the flash of light itself or to the electronic flash unit discharging the light. Most current flash units are electronic, having evolved from single-use flashbulbs and flammable powders. Modern cameras often activate flash units automatically.

Flash units are commonly built directly into a camera. Some cameras allow separate flash units to be mounted via a standardized "accessory mount" bracket (a hot shoe). In professional studio equipment, flashes may be large, standalone units, or studio strobes, powered by special battery packs or connected to mains power. They are either synchronized with the camera using a flash synchronization cable or radio signal, or are light-triggered, meaning that only one flash unit needs to be synchronized with the camera, and in turn triggers the other units, called slaves.

Fluorescent lamp

A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the lamp to glow. A fluorescent lamp converts electrical energy into useful light much more efficiently than incandescent lamps. The typical luminous efficacy of fluorescent lighting systems is 50–100 lumens per watt, several times the efficacy of incandescent bulbs with comparable light output.

Fluorescent lamp fixtures are more costly than incandescent lamps because they require a ballast to regulate the current through the lamp, but the lower energy cost typically offsets the higher initial cost. Compact fluorescent lamps are now available in the same popular sizes as incandescents and are used as an energy-saving alternative in homes.

Because they contain mercury, many fluorescent lamps are classified as hazardous waste. The United States Environmental Protection Agency recommends that fluorescent lamps be segregated from general waste for recycling or safe disposal, and some jurisdictions require recycling of them.

Globe (human eye)

The globe of the eye, or bulbus oculi, is the eyeball apart from its appendages. A hollow structure, the bulbus oculi is composed of a wall enclosing a cavity filled with fluid with three coats: the sclera, choroid, and the retina. Normally, the bulbus oculi is bulb-like structure. However, the bulbus oculi is not completely spherical. Its anterior surface, transparent and more curved, is known as the cornea of the bulbus oculi.


Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals.

The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and fine vellus hair. Most common interest in hair is focused on hair growth, hair types, and hair care, but hair is also an important biomaterial primarily composed of protein, notably alpha-keratin.

Attitudes towards different forms of hair, such as hairstyles and hair removal, vary widely across different cultures and historical periods, but it is often used to indicate a person's personal beliefs or social position, such as their age, sex, or religion.

Halogen lamp

A halogen lamp, also known as a tungsten halogen, quartz-halogen or quartz iodine lamp, is an incandescent lamp consisting of a tungsten filament sealed into a compact transparent envelope that is filled with a mixture of an inert gas and a small amount of a halogen such as iodine or bromine. The combination of the halogen gas and the tungsten filament produces a halogen cycle chemical reaction which redeposits evaporated tungsten to the filament, increasing its life and maintaining the clarity of the envelope. For this to happen, a halogen lamp must be operated at a higher envelope temperature (250° C; 482° F) than a standard vacuum incandescent lamp of similar power and operating life; this also produces light with higher luminous efficacy and color temperature. The small size of halogen lamps permits their use in compact optical systems for projectors and illumination. The small glass envelope may be enclosed in a much larger outer glass bulb for a bigger package; the outer jacket will be at a much lower and safer temperature, and it also protects the hot bulb from harmful contamination and makes the bulb mechanically more similar to a conventional lamp that it might replace.Standard and halogen incandescent bulbs are much less efficient than LED and compact fluorescent lamps, and have been banned in many jurisdictions because of this.


A hygrometer () is an instrument used to measure the amount of humidity and water vapor in the atmosphere, in soil, or in confined spaces. Humidity measurement instruments usually rely on measurements of some other quantity such as temperature, pressure, mass, a mechanical or electrical change in a substance as moisture is absorbed. By calibration and calculation, these measured quantities can lead to a measurement of humidity. Modern electronic devices use temperature of condensation (called the dew point), or changes in electrical capacitance or resistance to measure humidity differences. The first crude hygrometer was invented by the Italian Renaissance polymath Leonardo da Vinci in 1480 and a more modern version was created by Swiss polymath Johann Heinrich Lambert in 1755. Later in the year 1783, Swiss physicist and Geologist, Horace Benedict De Saussure invented the first hygrometer using human hair to measure humidity.

The maximum amount of water vapor that can be held in a given volume of air (saturation) varies greatly by temperature; cold air can hold less mass of water per unit volume than hot air. Temperature can change humidity. Most instruments respond to (or are calibrated to read) relative humidity (RH), which is the amount of water relative to the maximum at a particular temperature expressed as per cent.

Incandescent light bulb

An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated to such a high temperature that it glows with visible light (incandescence). The filament is protected from oxidation with a glass or fused quartz bulb that is filled with inert gas or a vacuum. In a halogen lamp, filament evaporation is slowed by a chemical process that redeposits metal vapor onto the filament, thereby extending its life.

The light bulb is supplied with electric current by feed-through terminals or wires embedded in the glass. Most bulbs are used in a socket which provides mechanical support and electrical connections.

Incandescent bulbs are manufactured in a wide range of sizes, light output, and voltage ratings, from 1.5 volts to about 300 volts. They require no external regulating equipment, have low manufacturing costs, and work equally well on either alternating current or direct current. As a result, the incandescent bulb is widely used in household and commercial lighting, for portable lighting such as table lamps, car headlamps, and flashlights, and for decorative and advertising lighting.

Incandescent bulbs are much less efficient than other types of electric lighting; incandescent bulbs convert less than 5% of the energy they use into visible light, with standard light bulbs averaging about 2.2%. The remaining energy is converted into heat. The luminous efficacy of a typical incandescent bulb for 120 V operation is 16 lumens per watt, compared with 60 lm/W for a compact fluorescent bulb or 150 lm/W for some white LED lamps.Some applications of the incandescent bulb (such as heat lamps) deliberately use the heat generated by the filament. Such applications include incubators, brooding boxes for poultry, heat lights for reptile tanks, infrared heating for industrial heating and drying processes, lava lamps, and the Easy-Bake Oven toy. Incandescent bulbs typically have short lifetimes compared with other types of lighting; around 1,000 hours for home light bulbs versus typically 10,000 hours for compact fluorescents and 30,000 hours for lighting LEDs.

Incandescent bulbs have been replaced in many applications by other types of electric light, such as fluorescent lamps, compact fluorescent lamps (CFL), cold cathode fluorescent lamps (CCFL), high-intensity discharge lamps, and light-emitting diode lamps (LED). Some jurisdictions, such as the European Union, China, Canada and United States, are in the process of phasing out the use of incandescent light bulbs while others, including Colombia, Mexico, Cuba, Argentina and Brazil, have prohibited them already.

List of root vegetables

Root vegetables are underground plant parts eaten by humans as food. Although botany distinguishes true roots (such as taproots and tuberous roots) from non-roots (such as bulbs, corms, rhizomes, and tubers, although some contain both hypocotyl and taproot tissue), the term "root vegetable" is applied to all these types in agricultural and culinary usage.Root vegetables are generally storage organs, enlarged to store energy in the form of carbohydrates. They differ in the concentration and the balance among starches, sugars, and other types of carbohydrate. Of particular economic importance are those with a high carbohydrate concentration in the form of starch; starchy root vegetables are important staple foods, particularly in tropical regions, overshadowing cereals throughout much of Central Africa, West Africa and Oceania, where they are used directly or mashed to make fufu or poi.

Many root vegetables keep well in root cellars, lasting several months. This is one way of storing food for use long after harvest, which is especially important in nontropical latitudes, where winter is traditionally a time of little to no harvesting. There are also season extension methods that can extend the harvest throughout the winter, mostly through the use of polytunnels.

Adherents of Jainism do not eat root vegetables.

Mercury-vapor lamp

A mercury-vapor lamp is a gas discharge lamp that uses an electric arc through vaporized mercury to produce light. The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger borosilicate glass bulb. The outer bulb may be clear or coated with a phosphor; in either case, the outer bulb provides thermal insulation, protection from the ultraviolet radiation the light produces, and a convenient mounting for the fused quartz arc tube.

Mercury vapor lamps are more energy efficient than incandescent and most fluorescent lights, with luminous efficacies of 35 to 65 lumens/watt. Their other advantages are a long bulb lifetime in the range of 24,000 hours and a high intensity, clear white light output. For these reasons, they are used for large area overhead lighting, such as in factories, warehouses, and sports arenas as well as for streetlights. Clear mercury lamps produce white light with a bluish-green tint due to mercury's combination of spectral lines. This is not flattering to human skin color, so such lamps are typically not used in retail stores. "Color corrected" mercury bulbs overcome this problem with a phosphor on the inside of the outer bulb that emits white light, offering better color rendition.

They operate at an internal pressure of around one atmosphere and require special fixtures, as well as an electrical ballast. They also require a warm-up period of 4 – 7 minutes to reach full light output. Mercury vapor lamps are becoming obsolete due to the higher efficiency and better color balance of metal halide lamps.

Olfactory bulb

The olfactory bulb (Latin: bulbus olfactorius) is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OFC) and the hippocampus where it plays a role in emotion, memory and learning. The bulb is divided into two distinct structures: the main olfactory bulb and the accessory olfactory bulb. The main olfactory bulb connects to the amygdala via the piriform cortex of the primary olfactory cortex and directly projects from the main olfactory bulb to specific amygdala areas. The accessory olfactory bulb resides on the dorsal-posterior region of the main olfactory bulb and forms a parallel pathway. Destruction of the olfactory bulb results in ipsilateral anosmia, while irritative lesions of the uncus can result in olfactory and gustatory hallucinations.


The onion (Allium cepa L., from Latin cepa "onion"), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus Allium. Its close relatives include the garlic, leek, chive, and Chinese onion.This genus also contains several other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion (Allium fistulosum), the tree onion (A. ×proliferum), and the Canada onion (Allium canadense). The name "wild onion" is applied to a number of Allium species, but A. cepa is exclusively known from cultivation. Its ancestral wild original form is not known, although escapes from cultivation have become established in some regions. The onion is most frequently a biennial or a perennial plant, but is usually treated as an annual and harvested in its first growing season.

The onion plant has a fan of hollow, bluish-green leaves and its bulb at the base of the plant begins to swell when a certain day-length is reached. The bulbs are composed of shortened, compressed, underground stems surrounded by fleshy modified scale (leaves) that envelop a central bud at the tip of the stem. In the autumn (or in spring, in the case of overwintering onions), the foliage dies down and the outer layers of the bulb become dry and brittle. The crop is harvested and dried and the onions are ready for use or storage. The crop is prone to attack by a number of pests and diseases, particularly the onion fly, the onion eelworm, and various fungi cause rotting. Some varieties of A. cepa, such as shallots and potato onions, produce multiple bulbs.

Onions are cultivated and used around the world. As a food item, they are usually served cooked, as a vegetable or part of a prepared savoury dish, but can also be eaten raw or used to make pickles or chutneys. They are pungent when chopped and contain certain chemical substances which irritate the eyes.

Series and parallel circuits

Components of an electrical circuit or electronic circuit can be connected in series, parallel, or series-parallel. The two simplest of these are called series and parallel and occur frequently. Components connected in series are connected along a single conductive path, so the same current flows through all of the components but voltage is dropped (lost) across each of the resistances. In a series circuit, the sum of the voltages consumed by each individual resistance is equal to the source voltage. Components connected in parallel are connected along multiple paths so that the current can split up; the same voltage is applied to each component.A circuit composed solely of components connected in series is known as a series circuit; likewise, one connected completely in parallel is known as a parallel circuit.

In a series circuit, the current that flows through each of the components is the same, and the voltage across the circuit is the sum of the individual voltage drops across each component. In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the flowing through each component.Consider a very simple circuit consisting of four light bulbs and a 12-volt automotive battery. If a wire joins the battery to one bulb, to the next bulb, to the next bulb, to the next bulb, then back to the battery in one continuous loop, the bulbs are said to be in series. If each bulb is wired to the battery in a separate loop, the bulbs are said to be in parallel. If the four light bulbs are connected in series, the same amperage flows through all of them and the voltage drop is 3-volts across each bulb, which may not be sufficient to make them glow. If the light bulbs are connected in parallel, the currents through the light bulbs combine to form the current in the battery, while the voltage drop is 12-volts across each bulb and they all glow.

In a series circuit, every device must function for the circuit to be complete. If one bulb burns out in a series circuit, the entire circuit is broken. In parallel circuits, each light bulb has its own circuit, so all but one light could be burned out, and the last one will still function.


Tulips (Tulipa) form a genus of spring-blooming perennial herbaceous bulbiferous geophytes (having bulbs as storage organs). The flowers are usually large, showy and brightly coloured, generally red, pink, yellow, or white (usually in warm colours). They often have a different coloured blotch at the base of the tepals (petals and sepals, collectively), internally. Because of a degree of variability within the populations, and a long history of cultivation, classification has been complex and controversial. The tulip is a member of the Liliaceae (lily) family, along with 14 other genera, where it is most closely related to Amana, Erythronium and Gagea in the tribe Lilieae. There are about 75 species, and these are divided among four subgenera. The name "tulip" is thought to be derived from a Persian word for turban, which it may have been thought to resemble. Tulips originally were found in a band stretching from Southern Europe to Central Asia, but since the seventeenth century have become widely naturalised and cultivated (see map). In their natural state they are adapted to steppes and mountainous areas with temperate climates. Flowering in the spring, they become dormant in the summer once the flowers and leaves die back, emerging above ground as a shoot from the underground bulb in early spring.

While tulips had probably been cultivated in Asia from the tenth century, they did not come to the attention of the West until the sixteenth century, when Western diplomats to the Ottoman court observed and reported on them. They were rapidly introduced into Europe and became a frenzied commodity during Tulip mania. Tulips were frequently depicted in Dutch Golden Age paintings, and have become associated with the Netherlands, the major producer for world markets, ever since. In the seventeenth century Netherlands, during the time of the Tulip mania, an infection of tulip bulbs by the tulip breaking virus created variegated patterns in the tulip flowers that were much admired and valued. While truly broken tulips do not exist anymore, the closest available specimens today are part of the group known as the Rembrandts – so named because Rembrandt painted some of the most admired breaks of his time.Breeding programs have produced thousands of hybrid and cultivars in addition to the original species (known in horticulture as botanical tulips). They are popular throughout the world, both as ornamental garden plants and as cut flowers.

Tulip mania

Tulip mania (Dutch: tulpenmanie) was a period in the Dutch Golden Age during which contract prices for some bulbs of the recently introduced and fashionable tulip reached extraordinarily high levels and then dramatically collapsed in February 1637. It is generally considered the first recorded speculative bubble; although some researchers have noted that the Kipper und Wipper (literally "Tipper and See-Saw") episode in 1619–1622, a Europe-wide chain of debasement of the metal content of coins to fund warfare, featured mania-like similarities to a bubble. In many ways, the tulip mania was more of a hitherto unknown socio-economic phenomenon than a significant economic crisis. Historically, it had no critical influence on the prosperity of the Dutch Republic, the world's leading economic and financial power in the 17th century. Also, from about 1600 to 1720 the Dutch had the highest per capita income in the world. The term "tulip mania" is now often used metaphorically to refer to any large economic bubble when asset prices deviate from intrinsic values.In Europe, formal futures markets appeared in the Dutch Republic during the 17th century. Among the most notable centered on the tulip market, at the height of tulip mania. At the peak of tulip mania, in February 1637, some single tulip bulbs sold for more than 10 times the annual income of a skilled craftsworker. Research is difficult because of the limited economic data from the 1630s, much of which come from biased and speculative sources. Some modern economists have proposed rational explanations, rather than a speculative mania, for the rise and fall in prices. For example, other flowers, such as the hyacinth, also had high initial prices at the time of their introduction, which immediately fell. The high asset prices may also have been driven by expectations of a parliamentary decree that contracts could be voided for a small cost, thus lowering the risk to buyers.

The 1637 event was popularized in 1841 by the book Extraordinary Popular Delusions and the Madness of Crowds, written by British journalist Charles Mackay. At one point 12 acres (5 ha) of land were offered for a Semper Augustus bulb. Mackay claims that many such investors were ruined by the fall in prices, and Dutch commerce suffered a severe shock. Although Mackay's book is a classic, his account is contested. Many modern scholars feel that the mania was not as extraordinary as Mackay described and argue that not enough price data is available to prove that a tulip-bulb bubble actually occurred.

Wet-bulb temperature

The wet-bulb temperature (WBT) is the temperature read by a thermometer covered in water-soaked cloth (wet-bulb thermometer) over which air is passed. At 100% relative humidity, the wet-bulb temperature is equal to the air temperature (dry-bulb temperature) and it is lower at lower humidity. It is defined as the temperature of a parcel of air cooled to saturation (100% relative humidity) by the evaporation of water into it, with the latent heat supplied by the parcel. A wet-bulb thermometer indicates a temperature close to the true (thermodynamic) wet-bulb temperature. The wet-bulb temperature is the lowest temperature that can be reached under current ambient conditions by the evaporation of water only.

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