EVOLUTION OF THE THERMOMETER
I. The Open Air-Thermometer of Galileo.
Discoveries and inventions are sometimes the product of the genius or of the intelligent industry of a single person and leave his hand in a perfect state, as was the case with the barometer invented by Torricelli, but more often the seed of the invention is planted by one, cultivated by others, and the fruit is gathered only after slow growth by some one who ignores the original sower. In studying the origin and tracing the history of certain discoveries of scientific and practical value one is often perplexed by encountering several claimants for priority, this is partly due to the circumstance that "coincidence of independent thought is often the cause of two or more persons reaching the same result" about the same time; and partly to the effort of each nation to secure for its own people credit and renown. Again, the origin of a prime invention is sometimes obscured by the failure of the discoverer to claim definitely the product of his inspiration owing to the fact that he himself failed to appreciate its high importance and its utility. The task of sketching the origin of the thermometer is fraught with similar difficulties; the actual inventor is known only at second hand, its development from a crude toy to an instrument of precision occupied more than a century, and its early history is encumbered with erroneous statements that have been reiterated with such dogmatism that they have received the false stamp of authority.
One of the most persistent of these errors is the assertion that the thermometer was invented about the year 1608 by a Hollander named Cornelius Drebbel. Wohlwill and Burckhardt have shown how this blunder originated. In 1624 a book was published at Pont-à-Mousson, entitled "La Récréation Mathématicque," over the pen-name A. van Etten, but written by the Jesuit Father Jean Leurechon, in which the author describes and figures a "thermometer, an instrument for measuring degrees of heat and cold that are in the air." The book was popular, passed through many editions and was translated into several languages; Casper Ens inserted in his "Thaumaturgus mathematicus," published at Cologne in 1651, a translation of the "76th Problem" of Leurechon, containing an account of the thermometer, and added to the word "instrumentum" the adjective "Drebbelianum." Reyer, Sturm, and others copied the phrase and it was incorporated in an article published in the "Journal des Sçavans," 1678, thus becoming a part of authoritative literature.
Ten years later, Dalencé, drawing his inspiration from the "Journal des Sçavans," published an attractive, illustrated volume entitled "Traittez des baromètres, thermomètres, et notiomètres, ou hygromètres, Amsterdam, 1688;" in this he wrote: "The thermometer was invented by a peasant of North Holland, named Drebbel," and he added that Drebbel was "called to the court of King James where he also invented the microscope." This statement was accepted by the Dutch savants Boerhaave and Musschenbroek, the French Abbé Nollet and others, and on their authority has been repeated over and over again, so that until very recently all encyclopedias, dictionaries of science and historical essays in natural philosophy adopted without reservation the phrase: "the thermometer was invented by Drebbel." And yet it is easy to show that the Hollander had no part in the invention and never claimed it, and that the error originated in the misinterpretation of a simple experiment described by Drebbel in a treatise on the "Elements."
Cornelius Drebbel, born in Alkmaar, Holland, 1572, was as alchemist who claimed to have discovered perpetual motion, and acquired sufficient reputation for learning to be invited to the court of James II, King of England; to him he dedicated his treatise on Primum mobile in 1607. Later in life he visited Prague where Rudolph had gathered famous alchemists, astrologers, and magicians, as well as more reputable astronomers, artists, antiquarians, and skilled mechanics; Drebbel, however, was unsuccessful in sustaining his claim to the discovery of perpetual motion, and Emperor Rudolph threw him into prison, from which he was released 'ere long by the death of the monarch, in 1612.
I have in my private library two copies of Drebbel's rare little volume, one in Dutch bearing the title: "Van de elementen quinta essentia en primum mobile, Amsterdam, 1709," and with a second title-page having the words: "Grondige oplossinge van de natuur en eyggenschappen der elementen, Amsterdam, 1732." The other copy is in German and bears the date 1715. (Poggendorff, the German historian of physics, admits never having seen an edition of this treatise by Drebbel.)
The Dutch version contains a full-page woodcut representing a retort hanging by a chain from a hook in a beam, the mouth of the retort is under water in a basin, and beneath it is a fire; on the surface of the water are seen bubbles of air issuing from the retort; the whole is observed by two men in out-door costume. The text accompanying this picture, when translated, reads as follows: "Heat makes air and water subtle and light; cold, as the opposite of heat, makes them smaller and presses them together and condenses all the air that the heat had made to rise, as may be clearly shown when a glass retort is hung with the mouth in a bucket of water and fire is placed under the belly. We shall then see that as soon as the air in the glass begins to get hot, that air rises out of the mouth of the retort, and the water gets full of bubbles, and this continues so long as the air gets hotter; but if the fire be removed from beneath the retort and the air begins to cool, then the air in the retort gets thicker and heavier, so that the retort fills with water, and if the glass was made very hot the water will completely fill it."
This simple experiment merely shows the expansion of air by heat and its contraction by cold, and there is no question whatever of measuring the amount of heat; besides, Drebbel had been anticipated by Hero of Alexandria, who described essentially the same phenomena 1,750 years before, and by Drebbel's contemporary della Porta.
Giambattista della Porta of Naples, the precocious author of "Magia Naturalis" (1558), is sometimes credited with the invention of the thermometer, owing to a passage in his book "I tre libri de spiritali," published at Naples in 1606. In this work he describes an experiment devised to measure the expansion of air when heated by a fire; the arrangement described is the same as Drebbel's retort and basin, but the cut accompanying the text shows an inverted matras with its mouth under water; Porta marked on the tube with pen and ink the highest and lowest points of the water-column, but he does not seem to have used the instrument as a heat-measurer.The word "thermoscope" first appears in print in the treatise "Sphæra mundi, seu Cosmographia demonstrativa," written in 1617 by Giuseppe Bianconi and printed at Bologna in 1620.
The word "thermometer" is first found in Leurechon's "Récréation mathématicque," (1624) already mentioned; his description of the instrument is the earliest that gives a clear notion of those in current use at the beginning of the seventeenth century, and is marked by charming simplicity of language.
"It is an instrument of glass which has a little bulb above and a long neck below, or better a very slender tube, and it ends beneath in a vase full of water, or it is curved behind and has another little bulb into which water or any other liquid may be poured... It is used thus: Put into the vase below some liquid colored blue, or red, or yellow, or other color not too dark, like vinegar, wine, or reddened water, or aqua fortis which has been used to etch copper. Having done this, I say in the first place that as the air enclosed in the bulb becomes rarefied or condensed the water will plainly ascend or descend in the tube; this you can easily test by carrying the instrument from a very hot place to a very cold one. But without disturbing its position, if you lay your hand gently on the upper bulb, it is so sensitive and the air is so susceptible to every impression, that you will instantly see the water descend, and on removing the hand the water will return to its place. It is still more sensitive if one warms the bulb with his breath, as if one wished to speak a word into its ear to command the water to descend.
"The reason of this motion is that the air heated in the tube rarefies and dilates and wishes to have more room, and therefore presses upon the water and makes it descend. On the other hand when the air is cooled and condenses it begins to occupy less space and fearing to leave nothing but a vacuum, the water ascends at once.
"I say in the second place that by this means one can know the degrees of heat and of cold that are in the air at each hour of the day, the air that is enclosed in the bulb rarefies or condenses, ascends or descends. Thus you see in the morning the water stands quite high, and it descends little by little up to midday; towards vespers it remounts. Thus in winter it ascends so high that it nearly fills the tube; but in summer it descends so low that in great heat it can scarcely be seen in the tube.
"Those who wish to determine these changes by numbers and degrees draw a line all along the tube and divide it into eight degrees, according to the philosophers, or into four degrees according to the physicians, subdividing each of the eight spaces into eight others so as to make sixty-four little ones. And by this means they can determine to what degree the water ascends in the morning, at midday and at every hour.
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| Leurechon's thermometers. |
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."
This interesting account is accompanied by two illustrations, copies of which are here given.
Credit for the invention of the primitive form of the thermometer really belongs to the famous Italian physicist and astronomer Galileo Galilei, notwithstanding he made no claim to having devised the instrument and his extant writings contain only a casual allusion to it. It must be remembered, however, that most of the manuscripts of Galileo have been lost; many were consigned to the flames by his own grandson, Cosimo, and those rescued by his pupil, Viviani, were edited only in part, the precious originals being scattered by the ignorant persons into whose possession they came. In the voluminous correspondence that Galileo carried on with contemporary savants, there is abundant evidence that he was the inventor of the thermometer, that he used it in scientific research and labored to improve its efficiency, as he had done for the pendulum, the compass, the telescope, and the microscope.
Viviani, in his Life of Galileo, published in 1718, says that about the time Galileo took possession of the chair of mathematics in Padua, which was at the end of the year 1592, he invented the thermometer, a glass containing air and water which served to indicate changes and differences in temperature, an instrument afterwards perfected by Ferdinand II, of Tuscany. This assertion is confirmed in letters addressed to Galileo by his friend Francesco Sagredo, of Venice, and made public by Nelli in his biography of Galileo. The first of these letters is dated 9 May, 1613. Sagredo writes: "The instrument for measuring heat, which you invented, I have made in several convenient styles, so that the difference in temperature between one place and another can be determined up to 100 degrees." And he then gives examples of phenomena that he has examined by the aid of the instrument.
Two years later, 7 February, 1615, Sagredo wrote to Galileo more fully: "The use of the instrument for measuring heat and cold has been improved by me, and I think there is opportunity for many observations, but without your cooperation I had hardly succeeded. With this instrument I see clearly that the water of our fountain is colder in winter than in summer, and I imagine that the same is true of springs and subterranean places, although our feelings seem to indicate the contrary. … During two snowstorms my instrument in a room here showed 130 degrees more heat than it indicated two years ago during extreme cold; on plunging the instrument into snow it indicated 30 degrees less, therefore only 100, but immersed in snow and salt, it showed a further 100 degrees less, and I believe in reality it marked still less but the snow and salt prevented it being seen clearly. In the greatest heat of summer the instrument stood at 360 degrees, and hence it appears that snow and salt increase the cold about one-third of the difference between extreme heat of summer and extreme cold of winter, a remarkable fact the reason for which I cannot determine. I shall learn with pleasure your opinions, especially what you have observed of the cold produced by saltpetre, of which I have heard many things, but have not personally seen. It will be difficult to send the instrument direct to you; it would be easier, I think, to have one made there."
A month later (15 March), Sagredo wrote to Galileo: "I have daily altered and improved the instrument for measuring temperature; if I could speak with you in person I could tell you from the beginning the whole history of my invention, or rather of my improvements. But since, as you write to me, and as I steadfastly believe, you are the first to discover and make the instrument, I suppose that those made by you and your excellent workmen are superior to my own; therefore I beg you at the first opportunity to write to me how you have them made, and I will report to you more or less of what is happening here."
In a long letter to Galileo, written 11 April same year, Sagredo mentions the use of wine as well as of water in the thermometers, alludes to having them made at the glass works in Murano, near Venice, and describes the construction of the best and most perfect of his instruments. This was made of a glass tube a finger wide joined to a bulb having a capacity of "three or four drinking glasses;" having made three of different sizes he watched their behavior during one year, sometimes as often as eight times a day, and he expresses wonder at their close agreement in both the extremes of cold and heat, the difference between them being not more than two or three degrees. He expresses surprise also at the great delicacy of his thermometers, which showed a difference of temperature when moved from the interior of a room to the open door, or on approaching them to a person or a lamp. He remarks at the same time that instruments made of thick and of thin glass do not change with equal rapidity, the thinnest moving the quickest; he also surmises that the unequal viscosity of water and of wine makes a difference. This interesting letter concludes with the remark: "Signor Gageo is in my room and disturbs me, and I do not want him to see what I am writing, so my letter will be disconnected for my mind is occupied in several ways."
The instrument Galileo used is described in a letter written by Father Castelli to Monsignor Cesarini, dated 20th September, 1638, in which he says it was used in public lectures thirty-five years before. Recounting what he remembers seeing, he writes: "Galileo took a glass vessel about the size of a hen's egg, fitted to a tube the width of a straw and about two spans long; he heated the glass bulb in his hands and turned the glass upside down so that the tube dipped in water held in another vessel; as soon as the ball cooled down the water rose in the tube to the height of a span above the level in the vessel; this instrument he used to investigate degrees of heat and cold." This lecture experiment dates from 1603.
In Galileo's extant writings there is only one reference to the thermometer and this corresponds in time with the letters of his friend Sagredo. In this fragment Galileo tries to explain the principle of the thermometer; he says that "when the air in the bulb contracts through cold, the wine in the stem rises to take the place of the void thus formed, and when the air is warmed it is rarefied and takes up more space so that it drives out and presses down the wine; "from this," says Galileo, "it follows that cold is nothing but absence of heat."
This correspondence and this fragment establish several things: 1st. The thermometer was invented by Galileo Galilei, between the years 1592 and 1597. 2nd. The instrument was an inverted air thermoscope containing either water or wine, and provided with a scale of degrees. 3rd. By its use Galileo determined relative temperatures of different places and of the same place at different seasons. 4th. Galileo made thermometric observations of freezing mixtures.
Galileo's method of graduating the stem cannot be ascertained, and was undoubtedly arbitrary, but the fact that he cites "degrees" prove that the instrument was of a higher type than some thermoscopes of even a later date.
Inverted air thermometers of this construction were, of course, subject to changes in atmospheric pressure, and were properly speaking "baro-thermoscopes," and no two of them were comparable. Sealed thermometers depending upon the expansion of liquids and independent of air pressure, were not made until fifty years later, and instruments with fixed points capable of accurate comparison were not devised until a century had elapsed.
The savants of Italy contemporary with Galileo naturally became acquainted with the great discoveries and inventions associated with his name, and the telescope from its marvelous revelations of celestial phenomena contributed the most to magnify his reputation; the great importance of the thermometer, on the other hand, was appreciated by comparatively few.
One of the colleagues of Galileo, Sanctorius Sanctorius Justipolitanus, who held the chair of the Theory of Medicine at the University of Padua from 1611 to 1624, applied the new instrument to physiological researches and described the results in several of his publications. The earliest of these references occur in his "Commentaries on the Medical Art of Galen," published in 1612, but written a year earlier, for the "license" is dated 9 June 1611. Nelli in his life of Galileo cites the following passage: "At last we have among us an instrument by which with a bulb we measure the withdrawal of heat from all the external parts of the body and of the air; by which we discover, very surely, how much more or how much less, daily, we differ from the normal [temperature]." Burckhardt cites this passage at second hand, transcribes the Latin erroneously, and says the sentence does not occur in the copy of Sanctorius' work found in the public library at Basel, and furthermore he satisfied himself that the volume contains no reference to any instrument for measuring heat; both these statements are undoubtedly correct so far as concerns the copy of Sanctorius which Burckhardt consulted, but I have found the passage in the copy of same date preserved in the United States Army Medical Library, Washington. The paragraph occurs in Part III, column 229, and this third part was probably wanting in the volume at Basel.
The historians of physics seem to have overlooked another passage of still greater interest which I discovered in the copy of Sanctorius at Washington. Translated it reads thus: "We determine the temperature by means of our glass instrument; we ascertain the high and the low (points) after this manner: we apply snow to the bulb of the glass instrument that the water may ascend to the highest point, then we approach the flame of a candle that the water may descend to the lowest point."
This important passage shows that Sanctorius appreciated the value of fixed points for graduation, and used snow and the heat of a candle to secure extremes. The division of the stem is unknown, but he mentions in one place (to be mentioned presently) "110 degrees."
One of the most celebrated books of Sanctorius is his "Medicina statica," published at Venice in 1614, and which passed through no less than eighteen Latin editions, besides two French versions, four English, one Italian, and one German. In the first edition occur the following interesting paragraphs: "How great the ponderousness of the air is, may in the first place be gathered from greater or less weight of the dregs of alum dried before in the sun and afterwards exposed to the air in the night time. Secondly, from our feeling a greater cold than what is observable in the weather-glass (instrumentum temperatorum). For the moisture or ponderousness of the air is to us the measure of its coldness. Thirdly, from the greater or lesser bending of a very thin board, especially
 Sanctorius' thermometer. |
if it be of a pear tree. Fourthly, from the contraction of the strings of a lute, or from hemp." (Section II, Aphorism IV, English translation by J. D., London, 1678.)
In this "aphorism" Sanctorius mentions three hygroscopes and one thermoscope. Parenthetically, I call attention to the use of burnt alum and of a balance to determine atmospheric moisture quantitatively.
The thermoscope used by Sanctorius is described by him in his "Commentaries on the first section of the first book of Avicenna," printed at Venice in 1646. In the preface to this the author says he has been engaged for fifteen years in preparing descriptions of his instruments, but the publication has been delayed by his duties as lecturer in the university. His apparatus resembled closely Galileo's, being a glass globe attached to a long narrow tube partially filled with water, which stood in a small open vessel of water; when the air in the globe is warmed the water in the tube sinks, and on cooling it rises. Sanctorius says the instrument "was used by Hero for other purposes, but I have applied it to the determination of the warm and cold temperature of the air and of all parts of the body, as well as for testing the heat of persons in a fever."
Sanctorius had the thermometer made in a variety of forms for taking the temperature of different parts of the body; in one style the bulb was inserted in the mouth of the patient and the long S-shaped tube was divided into degrees; when so applied the bulb was allowed to be in place during "ten pulse-beats." Sanctorius was the first physician to recognize that the human body has a normal temperature, and to determine variations from it as an aid to diagnosis. He also attempted to ascertain the heat of the moon, but misinterpreted his results; we now know that his instruments were not sensitive enough for the purpose. He made an experiment to measure the relation between the heat of the sun and of the moon, and recorded that in sunlight the water in his thermometer fell "110 degrees in two pulse-beats."
Before dismissing the connection of Sanctorius with the thermometer I note that the Italian physician nowhere claims to have invented it; on the contrary, he calls it in his "Commentaries on Galen" a "most ancient instrument." (P. 538, edition 1612.)[1]
- ↑ Prof. Cleveland Abbe suggests that this instrument had doubtless been used to illustrate the expansion of air by heat for a long time previous to Galileo, who simply added a scale for the use of Sanctorius so that the physician could express the intensity of fevers.