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62-474: The U.S. Signal Service, a predecessor to the Weather Bureau, occupied the summit and kept records from 1870 to 1892. Starting in 1932, the current observatory began keeping records. On April 12, 1934, the observatory staff recorded a wind gust of 231 mph that at the time was the highest recorded wind speed in the world, a record that was held until 1996. The observatory's weather data have accumulated into

124-444: A bi-layered parallel fiber hygroscopic cell physiology to control the awn's movement for dispersal and self-burial of seeds. Alignment of cellulose fibrils in the awn's controlling cell wall determines direction of movement. If fiber alignments are tilted, non-parallel venation, a helix develops and awn movement becomes twisting (coiling) instead of bending; e.g. coiling occurs in awns of Erodium , and Hesperostipa . Hygroscopicity

186-503: A crunchy, crisp cookie (British English: biscuit) versus a soft, chewy cake. Sugars such as honey , brown sugar , and molasses are examples of sweeteners used to create moister and chewier cakes. Several hygroscopic approaches to harvest atmospheric moisture have been demonstrated and require further development to assess their potentials as a viable water source. Hygroscopic glues are candidates for commercial development. The most common cause of synthetic glue failure at high humidity

248-435: A device accurate thermometer calibration is even more important than for a two-bulb configuration. Various researchers have investigated the use of saturated salt solutions for calibrating hygrometers. Slushy mixtures of certain pure salts and distilled water have the property that they maintain an approximately constant humidity in a closed container. A saturated table salt ( sodium chloride ) bath will eventually give

310-606: A handle is manually spun in free air flow until both temperatures stabilize. This is sometimes used for field measurements, but is being replaced by more convenient electronic sensors. A whirling psychrometer uses the same principle, but the two thermometers are fitted into a device that resembles a ratchet or football rattle. Dew point is the temperature at which a sample of moist air (or any other water vapor ) at constant pressure reaches water vapor saturation. At this saturation temperature, further cooling results in condensation of water. Chilled mirror dewpoint hygrometers are some of

372-522: A hygrometer that uses a stretched human hair as its sensor. In the late 17th century, some scientists called humidity-measuring instruments hygroscopes ; that word is no longer in use, but hygroscopic and hygroscopy , which derive from it, still are. Crude hygrometers were devised and developed during the Shang dynasty in Ancient China to study weather. The Chinese used a bar of charcoal and

434-411: A lump of earth: its dry weight was taken, then compared with its damp weight after being exposed in the air. The differences in weight were used to tally the humidity level. Other techniques were applied using mass to measure humidity, such as when the air was dry, the bar of charcoal would be light, while when the air was humid, the bar of charcoal would be heavy. By hanging a lump of earth on one end of

496-506: A reading of approximately 75%. Other salts have other equilibrium humidity levels: Lithium chloride ~11%; Magnesium chloride ~33%; Potassium carbonate ~43%; Potassium sulfate ~97%. Salt solutions will vary somewhat in humidity with temperature and they can take relatively long times to come to equilibrium , but their ease of use compensates somewhat for these disadvantages in low precision applications, such as checking mechanical and electronic hygrometers. Hygroscopy Hygroscopy

558-408: A relative humidity accuracy of about ±1.2%. Older chilled-mirrors used a metallic mirror that needed cleaning and skilled labor. Newer implementations of chilled-mirrors use highly polished surfaces that do not require routine cleaning. More recently, spectroscopic chilled-mirrors have been introduced. Using this method, the dew point is determined with spectroscopic light detection which ascertains

620-422: A result of the heat of sublimation, the wet-bulb temperature will eventually be lower than the dry bulb, although this may take many minutes of continued use of the psychrometer. Relative humidity (RH) is computed from the ambient temperature, shown by the dry-bulb thermometer and the difference in temperatures as shown by the wet-bulb and dry-bulb thermometers. Relative humidity can also be determined by locating

682-425: A screw, a , and at the other passing over a pulley, c , being strained tight by a silk thread and weight, d . The pulley is connected to an index which moves over a graduated scale (e). The instrument can be made more sensitive by removing oils from the hair, such as by first soaking the hair in diethyl ether . A psychrometer, or a wet and dry-bulb thermometer, consists of two calibrated thermometers, one that

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744-415: A staff and a bar of charcoal on the other end, and attaching a fixed lifting string to the middle point to make the staff horizontal in dry air, an ancient hygrometer was made. The metal-paper coil hygrometer is very useful for giving a dial indication of humidity changes. It appears most often in inexpensive devices, and its accuracy is limited, with variations of 10% or more. In these devices, water vapor

806-412: A stress that curls the cover toward the laminated side. This is similar to the function of a thermostat's bimetallic strip . Inexpensive dial-type hygrometers make use of this principle using a coiled strip. Deliquescence is the process by which a substance absorbs moisture from the atmosphere until it dissolves in the absorbed water and forms a solution. Deliquescence occurs when the vapour pressure of

868-599: A strong affinity for water and tendency to absorb moisture from the atmosphere if exposed to it. Unlike hygroscopy, however, deliquescence involves absorbing sufficient water to form an aqueous solution . Most deliquescent materials are salts , including calcium chloride , magnesium chloride , zinc chloride , ferric chloride , carnallite , potassium carbonate , potassium phosphate , ferric ammonium citrate , ammonium nitrate , potassium hydroxide , and sodium hydroxide . Owing to their very high affinity for water, these substances are often used as desiccants , which

930-473: A sufficiently high flow of air over the wet bulb for the most accurate results. One of the most precise types of wet-dry bulb psychrometer was invented in the late 19th century by Adolph Richard Assmann (1845–1918); in English-language references the device is usually spelled "Assmann psychrometer." In this device, each thermometer is suspended within a vertical tube of polished metal, and that tube

992-472: A valuable climate record since. Temperature and humidity readings have been collected using a sling psychrometer , a simple device containing two mercury thermometers. Where most unstaffed weather stations have undergone technology upgrades, consistent use of the sling psychrometer has helped provide scientific precision to the Mount Washington climate record. The observatory makes prominent use of

1054-468: A viewing or imaging mode. It did begin that way, with the word hygroscope referring in the 1790s to measuring devices for humidity level. These hygroscopes used materials, such as certain animal hairs, that appreciably changed shape and size when they became damp. Such materials were then said to be hygroscopic because they were suitable for making a hygroscope. Eventually, the word hygroscope ceased to be used for any such instrument in modern usage , but

1116-590: A wide variety of other substances. If a compound dissolves in water, then it is considered to be hydrophilic . Zinc chloride and calcium chloride , as well as potassium hydroxide and sodium hydroxide (and many different salts ), are so hygroscopic that they readily dissolve in the water they absorb: this property is called deliquescence . Not only is sulfuric acid hygroscopic in concentrated form but its solutions are hygroscopic down to concentrations of 10% v/v or below. A hygroscopic material will tend to become damp and cakey when exposed to moist air (such as

1178-497: Is hygroscopic (tending toward retaining moisture); its length changes with humidity, and the length change may be magnified by a mechanism and indicated on a dial or scale . Swiss physicist and geologist Horace Bénédict de Saussure was the first to build such a hygrometer, in 1783. The traditional folk art device known as a weather house also works on this principle. It consists of a human hair eight or ten inches [20 or 25 cm] long, b c, Fig. 37, fastened at one extremity to

1240-405: Is a common mechanism of seed dispersal as the movement of dead tissues respond to hygrometric variation, e.g. spore release from the fertile margins of Onoclea sensibilis . Movement occurs when plant tissue matures, dies and desiccates, cell walls drying, shrinking; and also when humidity re-hydrates plant tissue, cell walls enlarging, expanding. The direction of the resulting force depends upon

1302-461: Is a general term used to describe a material's ability to absorb moisture from the environment. There is no standard quantitative definition of hygroscopicity, so generally the qualification of hygroscopic and non-hygroscopic is determined on a case-by-case basis. For example, pharmaceuticals that pick up more than 5% by mass, between 40 and 90% relative humidity at 25 °C, are described as hygroscopic, while materials that pick up less than 1%, under

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1364-430: Is absorbed by a salt-impregnated paper strip attached to a metal coil, causing the coil to change shape. These changes (analogous to those in a bimetallic thermometer ) cause an indication on a dial. There is usually a metal needle on the front of the gauge that will change where it points to. These devices use a human or animal hair under some tension. (Whalebone and other materials may be used in place of hair.) The hair

1426-470: Is also an application for concentrated sulfuric and phosphoric acids . Some deliquescent compounds are used in the chemical industry to remove water produced by chemical reactions (see drying tube ). Hygroscopy appears in both plant and animal kingdoms, the latter benefiting via hydration and nutrition. Some amphibian species secrete a hygroscopic mucus that harvests moisture from the air. Orb web building spiders produce hygroscopic secretions that preserve

1488-401: Is an instrument which measures the humidity of air or some other gas: that is, how much water vapor it contains. Humidity measurement instruments usually rely on measurements of some other quantities such as temperature, pressure, mass, and mechanical or electrical changes in a substance as moisture is absorbed. By calibration and calculation, these measured quantities can be used to indicate

1550-530: Is drawn between the concentric tubes, as well as through the inner one." It is very challenging, particularly at low relative humidity, to obtain the maximal theoretical depression of the wet-bulb temperature; an Australian study in the late 1990s found that liquid-in-glass wet-bulb thermometers were warmer than theory predicted even when considerable precautions were taken; these could lead to RH value readings that are 2 to 5 percent points too high. One solution sometimes used for accurate humidity measurement when

1612-431: Is dry and one that is kept moist with distilled water on a sock or wick. At temperatures above the freezing point of water, evaporation of water from the wick lowers the temperature , such that the wet-bulb thermometer will be at a lower temperature than that of the dry-bulb thermometer. When the air temperature is below freezing, however, the wet-bulb must be covered with a thin coating of ice, in order to be accurate. As

1674-399: Is in turn suspended within a second metal tube of slightly larger diameter; these double tubes serve to isolate the thermometers from radiant heating. Air is drawn through the tubes with a fan that is driven by a clockwork mechanism to ensure a consistent speed (some modern versions use an electric fan with electronic speed control). According to Middleton, 1966, "an essential point is that air

1736-416: Is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment , which is usually at normal or room temperature. If water molecules become suspended among the substance's molecules, adsorbing substances can become physically changed, e.g. changing in volume, boiling point , viscosity or some other physical characteristic or property of

1798-508: Is ±2% RH; uncalibrated, this is two to three times worse. Capacitive sensors are robust against effects such as condensation and temporary high temperatures, but subject to contamination , drift and aging effects. They are, however, suitable for many applications. In resistive hygrometers, the change in electrical resistance of a material due to humidity is measured. Typical materials are salts and conductive polymers . Resistive sensors are less sensitive than capacitive sensors –

1860-525: The International System of Quantities (length, time, amount of substance, electric current, temperature, luminous intensity, mass). When cost, space, or fragility are important, other types of electronic sensors are used, at the price of lower accuracy. Capacitive hygrometers measure the effect of humidity on the dielectric constant of a polymer or a metal oxide . When calibrated , their accuracy at relative humidities between 5% and 95%

1922-950: The Mt. Washington Auto Road , and the Mt. Washington Valley Chamber of Commerce . In 2011, EMS replaced L.L. Bean as the official outfitter of the Observatory. The United States Postal Service maintains a small post office for outgoing mail, located in the Sherman Adams building at the summit; the ZIP Code is 03589. Boucher, Norman (1981-02-24). "How Cold Was It?: Five Days at the Mount Washington Observatory" . The Boston Phoenix . Retrieved 2024-02-22 . 44°16′13″N 71°18′12″W  /  44.27028°N 71.30333°W  / 44.27028; -71.30333 Sling psychrometer A hygrometer

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1984-518: The World Meteorological Organization Guide, "The principle of the heated psychrometer is that the water vapor content of an air mass does not change if it is heated. This property may be exploited to the advantage of the psychrometer by avoiding the need to maintain an ice bulb under freezing conditions.". Since the humidity of the ambient air is calculated indirectly from three temperature measurements, in such

2046-662: The 67th Governor of New Hampshire , houses the observatory; it is closed to the public during the winter and hikers are not allowed inside the building except for emergencies and pre-arranged guided tours. The Mount Washington Observatory receives much of its support from contributing members. However, over the years the MWObs has also come to receive support from several company and organizational partners, including L.L. Bean , Eastern Mountain Sports (EMS), Cranmore Mountain Resort ,

2108-460: The absolute amount of water present, but relative humidity is a function of both temperature and absolute moisture content, so small temperature variations within the air in a test chamber will translate into relative humidity variations. In a cold and humid environment, sublimation of ice may occur on the sensor head, whether it is a hair, dew cell, mirror, capacitance sensing element, or dry-bulb thermometer of an aspiration psychrometer. The ice on

2170-426: The air temperature is below freezing is to use a thermostatically controlled electric heater to raise the temperature of outside air to above freezing. In this arrangement, a fan draws outside air past (1) a thermometer to measure the ambient dry-bulb temperature, (2) the heating element , (3) a second thermometer to measure the dry-bulb temperature of the heated air, then finally (4) a wet-bulb thermometer. According to

2232-635: The air. A light emitter and a light detector are arranged with a volume of air between them. The attenuation of the light, as seen by the detector, indicates the humidity , according to the Beer–Lambert law . Types include the Lyman-alpha hygrometer (using Lyman-alpha light emitted by hydrogen), the krypton hygrometer (using 123.58 nm light emitted by krypton ), and the differential absorption hygrometer (using light emitted by two lasers operating at different wavelengths, one absorbed by humidity and

2294-473: The amount of water per mole of gas. This is considered the most accurate primary method of measuring absolute humidity , and national standards based on it have been developed in US, UK, EU and Japan. However, the inconvenience of using such devices means they are usually only used to calibrate less accurate instruments, called Transfer Standards. An optical hygrometer measures the absorption of light by water in

2356-419: The architecture of the tissue and is capable of producing bending, twisting or coiling movements. Typical of hygroscopic movement are plant tissues with "closely packed long (columnar) parallel thick-walled cells (that) respond by expanding longitudinally when exposed to humidity and shrinking when dried (Reyssat et al., 2009)". Cell orientation, pattern structure (annular, planar, bi-layered or tri-layered) and

2418-449: The change in thermal conductivity of air due to humidity is measured. These sensors measure absolute humidity rather than relative humidity. A gravimetric hygrometer extracts the water from the air (or other gas) and weighs it separately, for example by weighing a desiccant before and after it has absorbed the water. The temperature, pressure and volume of the resulting dry gas are also measured, providing enough information to calculate

2480-469: The change in material properties is less, so they require more complex circuitry. The material properties also tend to depend both on humidity and temperature, which means in practice that the sensor must be combined with a temperature sensor. The accuracy and robustness against condensation vary depending on the chosen resistive material. Robust, condensation-resistant sensors exist with an accuracy of up to ±3% RH ( relative humidity ). In thermal hygrometers,

2542-609: The coating industry because the application of paint and other coatings may be very sensitive to humidity and dew point . Humidity measurement is among the most difficult problems in basic metrology. According to the WMO Guide, "The achievable accuracies [for humidity determination] listed in the table refer to good quality instruments that are well operated and maintained. In practice, these are not easy to achieve." Two thermometers can be compared by immersing them both in an insulated vessel of water (or alcohol, for temperatures below

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2604-419: The coefficient of hygroscopic contraction (CHC)—the difference between the two terms being a difference in sign convention. Differences in hygroscopy can be observed in plastic-laminated paperback book covers—often, in a suddenly moist environment, the book cover will curl away from the rest of the book. The unlaminated side of the cover absorbs more moisture than the laminated side and increases in area, causing

2666-557: The effects of the opposite-surface's cell orientation control the hygroscopic reaction. Moisture responsive seed encapsulations rely on valves opening when exposed to wetting or drying; discontinuous tissue structures provide such predetermined breaking points (sutures), often implemented via reduced cell wall thickness or seams within bi- or tri-layered structures. Graded distributions varying in density and/or cell orientation focus hygroscopic movement, frequently observed as biological actuators (a hinge function); e.g. pinecones ( Pinus spp. ),

2728-495: The express purpose of maintaining moisture content , hygroscopic materials are known as humectants . Materials and compounds exhibit different hygroscopic properties, and this difference can lead to detrimental effects, such as stress concentration in composite materials . The volume of a particular material or compound is affected by ambient moisture and may be considered its coefficient of hygroscopic expansion (CHE) (also referred to as CME, or coefficient of moisture expansion) or

2790-445: The freezing point of water) and stirring vigorously to minimize temperature variations. A high-quality liquid-in-glass thermometer if handled with care should remain stable for some years. Hygrometers must be calibrated in air, which is a much less effective heat transfer medium than is water, and many types are subject to drift so need regular recalibration. A further difficulty is that most hygrometers sense relative humidity rather than

2852-466: The humidity. A prototype hygrometer was invented by Leonardo da Vinci in 1480. Major improvements occurred during the 1600s; Francesco Folli invented a more practical version of the device, and Robert Hooke improved a number of meteorological devices including the hygrometer. A more modern version was created by Swiss polymath Johann Heinrich Lambert in 1755. Later, in the year 1783, Swiss physicist and geologist Horace Bénédict de Saussure invented

2914-403: The humidity. Modern electronic devices use the temperature of condensation (called the dew point ), or they sense changes in electrical capacitance or resistance . 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. Thus a change in the temperature can change

2976-432: The ice plant ( Aizoaceae spp. ) and the wheat awn ( Triticum spp. ), described below. Two angiospermae families have similar methods of dispersal, though method of implementation varies within family: Geraniaceae family examples are the common stork's-bill ( Erodium cicutarium ) and geraniums ( Pelargonium sp. ); Poaceae family, Needle-and-Thread ( Hesperostipa comata ) and wheat ( Triticum spp. ). All rely upon

3038-475: The intersection of the wet and dry-bulb temperatures on a psychrometric chart . The dry and wet thermometers coincide when the air is fully saturated, and the greater the difference the drier the air. Psychrometers are commonly used in meteorology , and in the heating, ventilation, and air conditioning (HVAC) industry for proper refrigerant charging of residential and commercial air conditioning systems. A sling psychrometer, which uses thermometers attached to

3100-452: The most precise instruments commonly available. They use a chilled mirror and optoelectronic mechanism to detect condensation on the mirror's surface. The temperature of the mirror is controlled by electronic feedback to maintain a dynamic equilibrium between evaporation and condensation, thus closely measuring the dew point temperature. An accuracy of 0.2 °C is attainable with these devices, which correlates at typical office environments to

3162-402: The nature of the condensation. This method avoids many of the pitfalls of the previous chilled-mirrors and is capable of operating drift free. Chilled-mirrors remain the reference measurement for calibration of other hygrometers. This is due to their fundamental first-principle nature that refers to the core of condensation physics and measures temperature, which is one of the base quantities of

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3224-646: The other not). Aside from greenhouses and industrial spaces, hygrometers are also used in some incubators , saunas , humidors and museums . They are also used in the care of wooden musical instruments such as pianos, guitars, violins, and harps which can be damaged by improper humidity conditions. Hygrometers play a big part in firefighting as the lower the relative humidity, the more vigorously fuels may burn. In residential settings, hygrometers are used to assist in humidity control (too low humidity can damage human skin and body, while too high humidity favors growth of mildew and dust mite ). Hygrometers are also used in

3286-405: The physical side, a physico-chemical process. Berthelot's principle of reversibility, briefly- that water dried from plant tissue could be restored hygroscopically, was published in "Recherches sur la desiccation des plantes et des tissues végétaux; conditions d'équilibre et de réversibilité," ( Annales de Chimie et de Physique , April 1903). Léo Errera viewed hygroscopicity from perspectives of

3348-553: The physicist and the chemist. His memoir "Sur l'Hygroscopicité comme cause de l'action physiologique à distance" ( Recueil de l'lnstitut Botanique Léo Errera, Université de Bruxelles , tome vi., 1906) provided a hygroscopy definition that remains valid to this day. Hygroscopy is "exhibited in the most comprehensive sense, as displayed Hygroscopic substances include cellulose fibers (such as cotton and paper), sugar , caramel , honey , glycerol , ethanol , wood , methanol , sulfuric acid , many fertilizer chemicals, many salts and

3410-485: The probe matches the reading to the saturation humidity with respect to ice at that temperature, i.e. the frost point. However, a conventional hygrometer is unable to measure properly under the frost point, and the only way to go around this fundamental problem is to use a heated humidity probe. Accurate calibration of the thermometers used is fundamental to precise humidity determination by the wet-dry method. The thermometers must be protected from radiant heat and must have

3472-569: The salt inside salt shakers during humid weather). Because of their affinity for atmospheric moisture , desirable hygroscopic materials might require storage in sealed containers. Some hygroscopic materials, e.g., sea salt and sulfates, occur naturally in the atmosphere and serve as cloud seeds , cloud condensation nuclei (CCNs). Being hygroscopic, their microscopic particles provide an attractive surface for moisture vapour to condense and form droplets. Modern-day human cloud seeding efforts began in 1946. When added to foods or other materials for

3534-1151: The same conditions are regarded as non-hygroscopic. The amount of moisture held by hygroscopic materials is usually proportional to the relative humidity. Tables containing this information can be found in many engineering handbooks and is also available from suppliers of various materials and chemicals. Hygroscopy also plays an important role in the engineering of plastic materials. Some plastics, e. g. nylon , are hygroscopic while others are not. Many engineering polymers are hygroscopic, including nylon , ABS , polycarbonate , cellulose , carboxymethyl cellulose , and poly(methyl methacrylate) (PMMA, plexiglas , perspex ). Other polymers, such as polyethylene and polystyrene , do not normally absorb much moisture, but are able to carry significant moisture on their surface when exposed to liquid water. Type-6 nylon (a polyamide ) can absorb up to 9.5% of its weight in moisture. The use of different substances' hygroscopic properties in baking are often used to achieve differences in moisture content and, hence, crispiness. Different varieties of sugars are used in different quantities to produce

3596-537: The slogan "Home of the World's Worst Weather", a claim that originated with a 1940 article by Charles Brooks (the man generally given the majority of credit for creating the Mount Washington Observatory), titled "The Worst Weather In the World" (even though the article concluded that Mt. Washington most likely did not have the world's worst weather). The Sherman Adams summit building, named for

3658-414: The solution that is formed is less than the partial pressure of water vapour in the air. While some similar forces are at work here, it is different from capillary attraction , a process where glass or other solid substances attract water, but are not changed in the process (e.g., water molecules do not become suspended between the glass molecules). Deliquescence, like hygroscopy, is also characterized by

3720-738: The stickiness and adhesion force of their webs. One aquatic reptile species is able to travel beyond aquatic limitations, onto land, due to its hygroscopic integument . Plants benefit from hygroscopy via hydration and reproduction – demonstrated by convergent evolution examples. Hygroscopic movement (hygrometrically activated movement) is integral in fertilization, seed/spore release, dispersal and germination. The phrase "hygroscopic movement" originated in 1904's " Vorlesungen Über Pflanzenphysiologie ", translated in 1907 as "Lectures on Plant Physiology" ( Ludwig Jost and R.J. Harvey Gibson , Oxford, 1907). When movement becomes larger scale, affected plant tissues are colloquially termed hygromorphs. Hygromorphy

3782-836: The substance. For example, a finely dispersed hygroscopic powder, such as a salt, may become clumpy over time due to collection of moisture from the surrounding environment. Deliquescent materials are sufficiently hygroscopic that they dissolve in the water they absorb, forming an aqueous solution . Hygroscopy is essential for many plant and animal species' attainment of hydration, nutrition, reproduction and/or seed dispersal . Biological evolution created hygroscopic solutions for water harvesting, filament tensile strength, bonding and passive motion – natural solutions being considered in future biomimetics . The word hygroscopy ( / h aɪ ˈ ɡ r ɒ s k ə p i / ) uses combining forms of hygro- (for moisture or humidity) and -scopy . Unlike any other -scopy word, it no longer refers to

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3844-679: The word hygroscopic (tending to retain moisture) lived on, and thus also hygroscopy (the ability to do so). Nowadays an instrument for measuring humidity is called a hygrometer ( hygro- + -meter ). Early hygroscopy literature began circa 1880. Studies by Victor Jodin ( Annales Agronomiques , October 1897) focused on the biological properties of hygroscopicity. He noted pea seeds, both living and dead (without germinative capacity), responded similarly to atmospheric humidity, their weight increasing or decreasing in relation to hygrometric variation. Marcellin Berthelot viewed hygroscopicity from

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