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mercury / thermometer

mercury. A certain metal, white like silver, liquid at common temperatures, and congealing at forty degrees below zero, on Fahrenheit’s scale; and having a specific gravity of 13.6; quicksilver; hydrargyum. It acts as a poison, and its compounds are largely used in medicine. It is found in nature usually in combination with sulphur, forming cinnabar; named by the alchemists after the god Mercury. — Webster, 1882

thermometer. An instrument for measuring temperature, founded on the principle that changes of temperature in bodies are accompanied by proportional changes in their volume or dimensions. The thermometer usually consists of a glass tube of capillary bore, terminating in a bulb, and containing mercury or alcohol, which, expanding or contracting according to the temperature to which it is exposed, indicates the degree of heat or cold by the position of the top of the liquid column on a graduated scale. — Webster, 1882

During most of the winter there was four to six feet of snow on the level, with mercury congealed in the thermometer a good part of the time. – C.B. MacDonald, writing about the Hard Winter of 1880-1881.

In These Happy Golden Years, Almanzo Wilder pauses to look at the mercury thermometer at Fuller’s Hardware, and he sees that “the mercury was all down in the bulb, below forty…” (see Chapter 8, “A Cold Ride”). By “below” forty, Almanzo meant that the mercury in the column above the bulb was beneath or lower than the mark for forty degrees below zero, Fahrenheit (or Celsius; they’re the exact same at forty below). Mercury freezes at about -38 degrees C., so Fuller’s thermometer would have been useless to indicate a colder air temperature. The Weather Bureau used alcohol thermometers to record such colder temperatures.

It is not known for certain if there was a thermometer outside Fuller’s Hardware, but there was certainly at least one thermometer in town during De Smet’s early years, as many newspaper articles mention such a device as well as specific temperature readings taken in town.

Although there was a weather Signal Service Station established shortly after the Hard Winter in Huron, Dakota Territory, about thirty miles west of De Smet, there was no official weather station in De Smet until 1889, when the Kingsbury County Bank roof was the spot where a combination of one to four signal flags were raised to indicate not only the approach of storms or sudden fall in temperature, but if fair weather was in the forecast. Banker Ruth and his brother were the first weathermen in De Smet.

Laura Ingalls Wilder also mentions a thermometer in her On the Way Home diary, including a temperature reading several times when the weather was particularly hot, until she reported on August 5, 1894, that the thermometer had been lost!



Mistaken Thermometers. A thermometer is not of itself a very interesting instrument, and under ordinary circumstances it is to most people about the least attractive of human inventions; but now and then, under some extraordinary stress of weather, the thermometer rises–or falls–to a position of prime importance. There are days and nights when its invention seems to outrank the inventions of gunpowder and the mariner’s compass, and when its swift mercury seems to earn its name by striving to run higher or lower than ever mercury or other creature ever went before. This morning, for instance, the first question in each household will not be in relation to the New York Senatorship, or the doing of the Illinois Legislature, or the condition of the foreign and domestic money markets, but simply as to the state of the thermometer; and one peculiarity of the case will be that no two thermometers in Chicago will be found to agree with each other. There will be real differences of temperature according to the place of exposure, but beyond that there will be the inevitable failure of any one pair of thermometers to tell precisely the same story, and those belonging to scientific observers will probably indicate a more moderate temperature than those in the hands of mere laymen, who do not consider the zero marks in connection with storm centers and atmospheric currents so much as they do in its occult relations to the coal-bin and to frozen fingers. Somehow the finely made instruments whose markings go into the record of the Smithsonian Institute and the Signal Service, have a sort of well-bred way of avoiding excesses in any direction, and they seem to try to make out that every place has a pretty equable temperature through the whole year. If the plebeian thermometer, with its German-silver scale, and its case of tin painted black, with a fixed ring at the top, registers about twenty-five degrees below zero, the more aristocratic instrument, of whose indications somebody keeps a record, will hardly ever mark more than seven or eight degrees below; and, on the other hand, when the hot weather of the summer sends the mercury of the poor but respectable thermometer away up above the hundredth degree, the better-bred tube will seem to check its little vein of quicksilver at about the figure of eighty-five or ninety degrees, before the bounds of propriety have been passed. It sometimes appears as though thermometers were banded together to impose on the credulity of the ignorant in times of exceptional heat or cold, for, although not agreeing among themselves as to details, they do agree in showing a temperature one way or the other considerably in excess of the exact truth.

It was to cure this instrumental mendacity as far as possible that the Royal Society of England established the Kew Observatory, “whose principal work for the last quarter of a century has been to furnish accurate comparisons of thermometers sent there by physicists, meteorologists, physicians and instrument-makers;” and, following its lead, the Managing Board of the Winchester Observatory of Yale College have organized a service of having the same purpose in view, concerning which Dr. Leonard Waldo has prepared the very interesting account lately published in the Popular Science Monthly.

Even thermometers that come from the most reputable makers usually show some errors, and the well-known change that comes with age frequently amounts to a degree and a half within two years from the time the thermometer is made. The heating of the thermometer itself, frequently occasions an erroneous reading to the extent of nearly a degree, and then there is to be added the original error in the graduation of the scale by not having the boiling and freezing points properly fixed, and the error arising from the variations in the size of the capillary tube. All these errors together, even in well-made instruments, may easily amount to as much as two or three degrees. Errors likely to be more serious, if not greater, than those in thermometers used for meteorological purposes, are the false readings of the “fever” thermometers in general use by physicians, which are said to read almost invariably too high. Sixty-eight thermometers of this description, tested at New Haven in June last, showed errors of excess in readings which ranged from one-tenth of a degree up to an occasional instance of as much as two degrees. These instruments were chosen to represent seven different makers, and may be taken to fairly indicate the liability to error in using fever-thermometers which have not been compared with authoritative standards. It is disheartening to think how many physicians, deceived by their thermometers, which, placed under their patients’ tongues, have indicated a degree or two of fever-heat greater than what existed, may have spoken discouraging words which have led sick men to give up the struggle and die of sheer hopelessness.

The work of the Yale observatory consists, in the first place, of preparing standard thermometers, and, in the second place, of comparing others that are sent for the purpose with these standards. The investigation of the standards themselves is by far the more tedious operation of the two, for it involves the establishing of the freezing and boiling points upon the scale by actual experiment and without comparison with any other instrument. A thermometer which is old enough to have passed through the progressive changes which take place in the first years after it is made, is kept for several days at the freezing-point of water, and the point at which the mercury then stands is marked as what is called the permanent freezing point, which is the zero of the centigrade scale, or thirty-two degrees of the Fahrenheit scale. The boiling point of water at the level of the sea and with a barometric pressure of 29.922 inches in the latitude of 45 degrees is the second point to be fixed in the scale of the thermometer. This is done by exposing the instrument to the steam of pure water, and, from the observed height of the barometer, the known elevation and latitude of the place of observation, the true boiling-point is computed from the observed one, and the scale-mark of 100 degrees centigrade, or 212 degrees Fahrenheit, is thus fixed. Having these two cardinal points located on the scale, the intermediate points are fixed by dividing the scale so that at every part of the tube the length of one degree shall measure an equal volume of mercury. The size of the tube never being exactly uniform, it follows that the spaces indicating the degrees will not be exactly uniform. This process, which is called the calibration of a thermometer, is usually accomplished by detaching a small portion of the column of mercury and measuring its length in different, and usually consecutive, parts of the tube.

For ascertaining the variations in the readings of other thermometers from the true readings, the instruments to be corrected are hung beside a standard instrument in a vessel which for the sake of uniformity in the various temperatures at which the test is to be made, is wholly immersed in another vessel of water, an the numerous readings that are taken at the high and low temperatures determine the corrections that are to be made in the markings of the graduated scale.

That this service of correcting thermometers is destined to be a popular one in this country is sufficiently indicated by the fact that already about 500 thermometers have been sent to the observatory for verification, and among the chief benefits of the undertaking, as Dr. Waldo suggests, will be the fact that the errors of every thermometer issued with a certificate will be on file at the observatory, so that uniformity of data can be obtained from observations of isolated meteorologists made with these instruments all over the country. — The Daily Inter Ocean (Chicago, Illinois), January 20, 1881, 4.


mercury (THGY 8; OTWH)

thermometer (THGY 8; PG)