Thermometer

“ The thermometer may be filled by the following method:—When the straight tube has been made the first dumb-bell is introduced and shaken down well towards the lower bulb, the tube is now bent to its final shape and the whole thermometer filled with alcohol as described on page 44. Now heat the thermometer to a little above the maximum temperature that it is intended to record, and pour clean mercury into the open bulb while holding the thermometer vertically. Allow to cool, and the mercury will be sucked down. ”

“ The making of accurate thermometers is a task attended with many difficulties, the principal one being the liability of the zero or freezing point varying constantly, so much so, that a thermometer that is perfectly correct to-day, if immersed in boiling water, will be no longer accurate ”

“ Ether is poured into the silver tube in sufficient quantity to cover the bulb of the thermometer. The ether is then agitated by breathing through the flexible tube until, by the rapid evaporation thus produced, a condensation of moisture takes place, readily observable on the bright polished silver surface, and the temperature indicated by the thermometer at that moment is the dew-point. ”

“ The instrument with which the observer can work to best advantage is the one with which he should be provided.
The minimum thermometer is for the purpose of registering the lowest temperature between settings. It is exposed in a nearly horizontal position with the bulb slightly higher than the opposite end of the tube. Inasmuch as winter minima are sometimes lower than the freezing temperature of mercury, and because the instrument here described requires a transparent column, minimum thermometers usually contain alcohol instead of mercury. ”

“ The cheap German paper-scale thermometers are largely used, fitted in wooden cases, as dairy thermometers, and a larger size for brewing purposes. Alarm thermometers are often employed, in which electric contact is made and a bell rung when the temperature exceeds or falls short of a certain limit. Thermostats of various forms are made use of, in which a thermometer, by the position of the mercury in the stem, regulates the gas-supply of a burner and thus the heat of an enclosure. ”

“ They have made thermometers with bulbs or reservoirs formed of about nine inches of excessively thin cylindrical glass, whose outer diameter is not more than a twentieth of an inch; so that, owing to the large surface presented, the indications are positively instantaneous. This form of thermometer was constructed expressly to meet the requirements of scientific balloon ascents, to enable thermometrical readings to be taken at the precise elevation. It was contemplated to procure a metallic thermometer, but on the production of this perfect instrument the idea was abandoned. ”

“ Few are aware of the errors found to exist even in the thermometers of reputable makers. The well-known change which takes place with age in every thermometer not infrequently amounts to a degree and a half Fahrenheit within two years from the time the thermometer is made. The change depending upon the temperature to which a thermometer is heated, even supposing this to be no greater than the boiling-point of water, may be three fourths of a degree. ”

“ It usually requires from a quarter to half an hour to put a minimum thermometer with a broken column in order. Great care must be used that no part of the alcohol remains in the chamber at the farther end of the tube.
Thermometer Shelter.—Maximum and minimum thermometers should be sheltered from the sun and from direct contact with precipitation of every sort. They also must be placed so that they are in contact with free air. They must be sheltered from heat radiated from buildings, metal roofs, and pavements. The board support should not be attached directly to the wall of a building ”

“ To make use of it, I put it in the sun, and sometimes in the hands of a fever patient, having filled it quite full of water except the neck; the heat expanding the water makes it ascend by a greater or less amount according to the great or little heat."
This evidently describes a water thermometer, or thermoscope, and so far embodied a new principle, yet it was still influenced by the pressure of the air. The instrument did not attract much attention. ”

“ Shortly after Réaumur's publication Joseph Nicolas de l'Isle, professor of astronomy in St. Petersburg, devised a thermometer on the same principles, but adopted as the point of departure the temperature of boiling water, calling it zero, and adjusting the scale so that the freezing-point of water equaled 150 degrees. ”

“ Upon placing the Thermometer in a favourable situation, in or against the body of a patient, owing to the amount of heat with which it there comes in contact, the mercury in the bulb expands, and the Index is pushed up to the highest point in the Thermometer that the heat of the body at that time is capable of causing, if the Thermometer is kept in contact with the body for the requisite time ”

“ I have now completed the task undertaken, viz., to sketch impartially the history of the evolution of the thermometer from its first beginnings in Italy, through its crude early forms down to the three standards now commonly used in all civilized lands. It is interesting to note: First, that no nation makes popular use of the thermometer designed by its own citizen. ”

“ Of no other maximum thermometer can it be said that it is impossible to derange or put it out of order; hence, as regards durability, it surpasses all others. Nothing short of actual breakage can cause it to fail. Hence it is the most easily portable of all self-registering thermometers, an advantage which renders it suitable for travellers, and for transmission abroad. In the year 1852, the British Meteorological Society reported this thermometer to be “the best which has yet been constructed for maximum temperature, and particularly for sun observations.” ”

“ Also one can determine how much colder one day is than another, noting how many degrees the water ascends and descends. One can compare the greatest heat and cold of one year with those of another year. One can ascertain how much hotter one room is than another; one can maintain a room at an equal temperature by making the water of the thermometer stand always at a certain degree. One can test also the intensity of fevers; in short, one can know pretty nearly to what extent air is rarefied in the greatest heat, and so forth. ”

“ For in order to be used in this form as real thermometers, they must be exposed on each occasion first of all to some zero level of temperature, say, that of melting ice. If we then take them into the region of temperature we want to measure, we shall discern the difference of levels through the corresponding movement of the column. The final position of the column tells us nothing in itself. It is always the change from one level to another that the thermometer registers - precisely as does the sense of warmth in our hands in the experiment just described. ”

“ In regard to the warmth of air, the thermometer is not an exact index of its temperature. For all bodies are constantly radiating their heat to cooler adjacent surfaces until all come to the same temperature. This being so, the thermometer is radiating its heat to walls and surrounding objects, in addition to what is subtracted by the air that surrounds it, and thus the air is really several degrees warmer than the thermometer indicates. A room at 70° by the thermometer is usually filled with air five or more degrees warmer than this. ”

“ Measurement of Lower Temperatures by the Thermo-electric Method.—Many cases arise in practice in which a thermal junction and a sensitive galvanometer are preferable to a mercury thermometer; and below -39° C., at which temperature mercury freezes, a thermal junction is frequently better to employ than an alcohol or pentane [97] thermometer. A number of practical examples of the use of thermal junctions for ordinary and low temperatures will now be considered. ”

“ The heat no longer affects the thermometer, because it is wholly employed in converting the ice into water. As the ice melts, the caloric becomes latent in the new-formed liquid, and therefore cannot raise its temperature; and the thermometer will consequently remain stationary, till the whole of the ice be melted. ”

“ Sensitive Thermometers.—Where quickness of reading is essential, the mercury thermometer, or the tube form of electric thermometer, is unsuitable. In cases where the thermometer has to be immersed in a conducting liquid or solution, the fine wire forming the bulb may be insulated by enclosing it in a coiled glass capillary. This method has been employed by Callendar and Barnes and by Jaeger, but the instrument is necessarily fragile, and requires careful handling. For non-conducting liquids or gases the bare wire may be employed with great advantage. ”

“ I do not think, however, that the degrees named will ever be exceeded in any fever.
"The scales of such thermometers as are used for determining the boiling-points of liquids begin also at 0° and run up to 600°, for at about this temperature mercury begins to boil. To increase the sensitiveness of thermometers they are made with cylinders instead of spheres, so that a larger surface will be more quickly affected."
Fahrenheit then gives a full account of his method of filling thermometers with liquids, a practical feature not necessary to detail in this place. ”

“ It consisted of a thermometer enclosed in a shaft of copper with a wooden handle, and a door in its side, by which the temperature can be ascertained with precision. It is needless to point out the superiority of this plan, over the common mode of determining this very essential point, by feeling of a stick previously stuck in the bed; the sensation of heat when the stick is grasped in the hand will obviously depend in a great degree upon the temperature of the hand itself. ”

“ I suspected that you would make these objections; and, in order to remove them, I enclosed two thermometers in the air-pump; one which stands in the glass of water, the other in the phial of ether; and you may see that the equilibrium of temperature is not destroyed; for as the thermometer descends in the water, that in the ether sinks in the same manner; so that both thermometers indicate the same temperature, though one of them is in a boiling, the other in a freezing liquid. ”

“ These degrees can be tested by an experienced hand without the aid of the thermometer, and the learner may accustom himself by trying them in the following manner: Take the stem of a clay pipe and dip it into the sugar as it boils, draw it out again and pass it through the forefinger and thumb; when it feels oily you will find by looking at your thermometer that it has reached the degree of smooth, 215 to 220 by the glass. ”

“ The thermodynamical correction of the gas thermometer, which amounts to half a degree at this point, is also to some extent uncertain, on account of the extrapolation. Provided, however, that some exact value of the S.B.P. is chosen for reference, for the reduction of observations with platinum thermometers, the results so reduced will be strictly comparable, and can be corrected at any subsequent time when the value of the S.B.P. is more accurately determined. ”

“ Nothing can illustrate more cogently the imperfections of the best instruments then in scientific hands, and the character of those in ordinary use can be imagined; nothing can better demonstrate the immense advance made by Fahrenheit, and even those who deprecate the wide use of his illogical scale must pay tribute to the value of his services in developing reliable thermometers. ”

“ Of this the "Saggi" say: "We can lay down no certain rule to make it practice, often trials being the only way to effect it; by increasing and diminishing the size of the bulb or the bore of the cane, or the quality of the liquor, till at length it hits it right."
IV. The fourth thermometer had a very long tube bent in the form of a spiral, made "rather for fancy and curiosity to see the liquor run the decimals of degrees by the only impulse of a warm breath than for any accurate deduction." This instrument is styled a "very ticklish thermometer." ”

“ Daddy Blake went to the door, outside of which hung an instrument called a thermometer. I guess you have seen them often enough. A thermometer is a glass tube, fastened to a piece of wood or perhaps tin, and inside is a thin, shiny column. This column is mercury, or quicksilver. Some thermometers have, instead of mercury, alcohol, colored red, so it can easily be seen.
You see mercury, or alcohol, will not freeze, except in much colder weather than you ever have where you live, unless you live at the North Pole. ”

“ With a mercury thermometer a continuous record of temperature can only be obtained by the aid of photography, a method which has been in use for many years at some first-class observatories, but which cannot be generally employed on account of the expense and the elaborate nature of the apparatus required. The commonest type of recording thermometer works on the principle of the Bourdon pressure-gauge. The bulb consists of a curved metallic tube filled with liquid, the expansion of which with rise of temperature tends to straighten the tube. ”

“ In using a thermometer below zero, the observer must pay attention to the change in the direction of reading the scale, the fractions of a degree counting downward from the degree mark instead of upward from it, as in readings above zero. Readings below the zero of the scale are distinguished in recording them by prefixing the minus sign. The annexed figure shows the reading of two thermometers graduated to fifths of a degree, one showing a temperature of 1°.4, the other of -1°.4. ”