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Our up-time characters are in Little Ice Age Europe now, and hence neither their experience with twentieth-century American agriculture nor their limited literature on twentieth-century European agriculture are a completely reliable guide as to what crops will grow where. The effect of the Ring of Fire on climate is also somewhat uncertain.
Airship lift depends on the difference in density between the lift gas and the ambient air, and thus in part on their respective temperatures. So temperature is relevant to airship pilots, not just farmers.
We need to start making accurate records of weather conditions, and we will certainly be looking at temperature, humidity, and precipitation.
In Grantville, the most common form of outdoor thermometer is the liquid expansion thermometer. Most such thermometers will probably use, as the "thermometric liquid," an organic liquid with a red or blue dye, but it will be common knowledge that mercury may also be used.
Mercury has the advantages of being opaque, easily purified, chemically stable, not wetting or chemically attacking glass, liquid over a wide temperature range (-38.8oC to 356.7oC, thus unlikely to evaporate at the top of the column), and having clearly defined meniscus, a high thermal conductivity, low specific heat (making it rapidly responsive to changes in temperature), and a fairly linear coefficient of thermal expansion. Unfortunately, it is poisonous, the expansion is small compared to alcohol, and in very cold climates it can solidify.
Several different organic liquids have been used, but the most readily available in the 1632 universe is ethanol, with a liquid range of -114 to 78oC. My prediction is that mercury will be used for a small number of precision reference thermometers and the actual weather stations will use ethanol thermometers.
Glass composition is also significant. It is not just the liquid, but also the glass, that expands as the temperature increases, and not entirely linearly (or at the same rate as the liquid). Also, after being first heated and then cooled, the glass bulb of some compositions did not return to its original dimensions, leading to a slow rise in the zero of mercury thermometers. In the late nineteenth century, Schott developed a series of more stable glasses, notably borosilicate (Pyrex(R) glass) (Vogel 21). Hard glasses are generally preferred (EB11/Thermometry).
Most modern meteorological thermometers have the stem, with engraved scale markings, inside a protective glass sheath, and there is a white enamel backing on the stem to make the liquid movement more visible. (Srivastava 96). My "hardware store" thermometers are unsheathed, and the scale is on a separate attached metal frame. The attached scale will "inevitably move slightly with time." (Burt 116).
The first thermometers sensed air rather than liquid expansion. The first known drawing of a thermometer is from 1611. It shows an inverted flask with a long narrow stem, fitting into the neck of a short-necked flask, the latter partially filled with water. The bottom of the stem of the first flask is below the liquid surface. A rise in temperature caused the expansion of the air in the short flask, pushing the water up the stem. Alongside the stem there was a scale divided first into eight degrees and these each into six ten-minute intervals. Its inventor, possibly living in Rome, is unknown (Middleton 11).
The basic problem with unsealed air thermometers was that the expansion of the air was a function of pressure as well as temperature. In 1632 Jean Rey (1583-OTL c1645) dispensed with the second flask, and turned the first flask stem upward, creating a liquid expansion thermometer. However, the tube was unsealed so errors could arise from evaporation of the water (27). The sealed spirit-in-glass thermometer is attributed to Ferdinand II, Grand Duke of Tuscany, and most likely invented in 1654. The first experiments with mercury were in 1657, but the Tuscan academicians deemed it inferior in performance (28-37).
Before leaving the subject of early temperature measurement, I wish to call the reader's attention to Fitzroy's chemical weather glass (1862), as is it the sort of curiosity that a resident of Grantville might have inherited, or picked up at a craft fair, before the Ring of Fire. It "consisted of a solution of camphor and certain inorganic salts in aqueous alcohol, sealed in a glass tube." Negretti & Zambra used potassium nitrate and ammonium chloride. The salts formed crystalline dendrites, and Fitzroy claimed that when the crystals built up, the weather would get colder and stormier, and if they disappeared, it would be dry and clear. Studies by Mills have shown that the chemical weather glass is sensitive both to the current temperature and "any preceding regime of temperature changes." It is thus a thermoscope. Mills comments, "A rapid fall in temperature associated with an approaching vigorous cold front could conceivably trigger ... rapid crystal growth if observed at a fortuitous time, but in general any correlation between appearance and future weather patterns would be purely coincidental."
Manufacture. In 1612, Giovanfrancesco Sangredo (d. 1620) made several thermoscopes, at a cost of four lire each. These had no scale, but the column height could be measured with a caliper. He apparently made use of "a wine glass with a foot, a small ampoule, and a glass tube," and he could make ten in an hour.
The Grand Duke's glassblower, Mariani, had incredible skill and was able to manufacture thermometers with a "50 degree range" (corresponding to the modern -18.75 to 55oC) with great consistency. He admitted, however, that he could not do this for the Medicean 100- and 300-degree range thermometers, because "inequalities could more easily occur in the larger bulb and longer tube" (Middleton 34-5). On the other hand, Middleton asserts that "workmen north of the Alps found it difficult enough at first to make a plain bulb and tube and fill it with spirit of wine" (132).
Roemer proposed that after forming the tube, it be examined for uniformity by examining the length of a drop of mercury as it passed down the bore. If the tube was found to be irregular, it was discarded, and if conical (the length increased or decreased at a constant rate), he took measurements and divided the bore into four equal volumes (67).
While in many thermometers the bulb was blown on the capillary tube, EB11/Thermometry recommends that it be formed of a separate piece of glass fused onto the stem.
Bimetallic Thermometers. In Grantville, there should also be thermometers with a dial readout. These have a strip with two different metals layered together, usually brass and iron. The metals have different coefficients of expansion and thus the strip bends toward the less responsive metal. The deflection is proportional to the temperature change and to the square of the length; winding the strip into a helix allows a long and thus more sensitive element to be relatively compact. A pointer is connected to the center. Generally speaking, they are less accurate than liquid expansion thermometers, and require weekly (if not daily) recalibration (Thermoworks), but they are the basis for the most common kind of thermograph.
Platinum Resistance Thermometers. These, known as RTDs (Resistance Temperature Detectors) rely on the change of electrical resistance with temperature. EB11/Thermometry provides formulae, circuit schematics, and comments on errors and corrections. The current levels must be kept very low (<1 ma) to minimize self-heating (Srivastava 135, 137).
In the twenty-first century, RTDs are available in two grades, "standard" and "industrial." RTDs will not be found in Grantville homes or schools, but it is conceivable that the power plant has them (most likely "industrial" grade). The standard RTDs are used as primary reference thermometers. They have platinum wire of 99.999% purity wound in a strain-free configuration (MINCO). Unfortunately, the strain-free resistance element is extremely delicate (Ripple), so SPRDs are used in laboratories.
The industrial grade RTDs use platinum of lower purity and also have a simpler construction in which the resistance element is supported (or thick enough to be self-supporting). When calibrated, they have an accuracy of perhaps 0.01oC, an order of magnitude less than the SPRTDs. But they are also cheaper to make and calibrate (Fluke).
There is a small quantity of platinum available in Grantville in the form of jewelry, and it may be sufficient for experimentation. Commercial development of RTDs will have to await platinum mining (see Cooper, Mineral Mastery, Grantville Gazette 23) and purification. Developers will have to worry not only about platinum purity, but also about mounting the wire so as to minimize the strain caused by thermal expansion and contraction (Price).
Even if the wire is not subject to chemical attack, it is mechanically fragile, and the wire is typically protected from the medium by encasing it in a glass, quartz, porcelain, or metal tube (Patranabis 223). A plastic cladding might also work. In any event, the sheathing increases the lag time (Srivastava).
Platinum's advantages are that it is a noble metal, with a high melting point, and that it has a very linear response over a wide temperature range. Copper is more responsive, and linear over the range -50 to 150oC, but subject to chemical attack. Nickel is even more responsive, and is chemically resistant, but there is no simple formula for calculation of its resistance (MINCO). One can scavenge the nichrome wire heating element from a defunct toaster or heating pad. However, nichrome actually has a rather low temperature sensitivity (Lemieux). My expectation is that the first NTL resistance thermometers will use copper wire.