# Evolution of the Thermometer/Chapter 2

II. Thermoscopes of the Accademia del Cimento.
Modifications and improvements of the thermoscope were probably made by many savants interested in their use, both in Italy, the birthplace of the instrument, and in all parts of Europe to which the knowledge of the invention penetrated, but few records of them have survived.
There is a manuscript preserved in the library of the Arsenal, Venice, entitled "Matematica meravigliosa," written by Telioux, a Roman engineer, in 1611, that is said by the historian ​Libri (Histoire des sciences mathématiques en Italie, Vol. IV, p. 471, notes), to describe a thermoscope independent of atmospheric pressure. The instrument is said to consist of a bulb with a neck a foot or more long, nearly filled with water into which a smaller bulb-tube was inverted so that the neck was beneath the surface; Libri's account is accompanied by a drawing that does not correspond with the description and is obviously incorrect; whether the figure is from Telioux' manuscript does not appear, but if it is of the date 1611, it is the earliest representation of a thermometer with scale known to me. The scale attached to each side of the stem is divided into eight large spaces, and each space into sixty smaller ones, a division probably suggested by the graduation of astronomical instruments into degrees and minutes.
According to Poggendorff , Salomon de Caus, whose name is associated with the use of steam as a mechanical power, described a very imperfect thermometer in the work "Raisons des forces mouvantes," published at Frankfurt in 1615.
The eminent Englishman, Lord Chancellor Bacon, is sometimes put forward as the ​inventor of the thermometer, but he merely alludes to the instrument as if well known. In the "Novum Organon," 1620, Bacon describes an inverted "heat-glass," styled "Vitrum calendare," and says it bore "attached to the stem a long narrow strip of paper marked off with degrees at pleasure."
Attempts have been made by Italian authors to secure the credit of inventing the thermometer for another Englishman, Robert Fludd de Fluctibus, a physician and mystic whose books show more erudition than common sense. The Jesuit Franciscus de Lanis, in a work dated 1670, named Fludd as the original inventor, and Clemente, in his life of Galileo, 1793, has the contemptible effrontery to claim that Galileo in 1603 used an instrument made by Fludd. The facts are that about the year 1603 Fludd visited many countries of Europe, including Italy, where he may well have seen the Galileo thermoscope known to savants in Padua. Twelve years after Fludd's return to England, in 1617, he published a work (Utriusque cosmi … historia) in which he described an experiment chiefly borrowed from Hero, of Alexandria. In another work (Philosophia Moysaica) issued in 1638, a year after ​his death, Fludd describes a "Speculum calendarium," which was a simple thermoscope of the usual pattern, and says he found it in a manuscript more than 500 years old. This certainly disposes of the pretensions of those who claim Fludd as an originator.
The instrument figured in Fludd's book represents the usual inverted air thermoscope in a basin of water, the stem being divided into fourteen degrees, of which seven are below and seven above a central line named "sphaera aequalitis," a curious forerunner of our modern zero with plus and minus degrees.
The list of those to whom the invention of the thermometer has been ascribed should include the Servite monk Fra Paolo Sarpi, named by Fulgenzio for the honor; "Father Paul," as he is called, does not seem to have used the instrument before 1617, and does not mention it in his writings.
Before the days of academies of science and of periodical literature, communication between European savants was maintained by personal visits and by correspondence. One of the most active intermediaries between scientists in the first half of the seventeenth century was a French theologian, Father Marin Mersenne; ​he was in constant communication with Galileo, Descartes, Gassendi, Roberval, Hobbes, and others, sending them news of discoveries and inventions in exchange for similar favors. Mersenne was also an experimenter, repeating and verifying the labors of others and thus familiarizing himself with every branch of physical science, but he made no noteworthy discovery; he was the originator of the custom of propounding prize questions, a scheme for stimulating scientific work afterwards adopted by certain learned societies. His "Récréations des savans" was published in 1634.
There lived at that time in Southern France an obscure physician named Jean Rey, who did two things in his lifetime that ought to have brought him renown, but he was in advance of the age and his discoveries were not appreciated by his contemporaries. Rey applied his knowledge of chemistry to the solution of the much vexed problem "why do lead and tin increase in weight when calcined?" In a book published on this subject in 1638, he gave the correct explanation, recognizing that the metals combined with a constituent of the air, and anticipating the grand truths that made Lavoisier famous 150 years later. ​Secondly, Rey was the first to make use of the expansion of a liquid in the construction of a thermometer. In a letter written to Father Mersenne, 1 January, 1632, he said: "I observe there are diverse kinds of thermoscopes and thermometers; what you tell me does not agree with mine, which is merely a small round flask having a very long slender neck. 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.
Mersenne himself devised a modification of the air thermoscope intended to increase its delicacy, and described it in a work published at Paris in 1644, four years before his death (Cogitata physico-mathematica). The instrument consisted of a narrow tube having a large bulb at one end and a small one at the other, the latter being pierced with a minute hole; ​by warming gently the air in the larger bulb
* Mersenne's thermometer.
while the smaller was plunged in water and then removing it, a few drops of the liquid rose in the graduated tube forming a short column of water that served as an indicator of changes of temperature. The graduation
* A Kircher's thermometer.
of the stem was peculiar; it was divided into eight degrees and these were numbered on one side from above down ward, and on the other in reverse order.
In 1643, the learned Jesuit Athanasius Kircher published a quarto entitled: "Magnes, sive de arte magnetica," in which he mentions several thermoscopes. They have the usual form of the water-air instruments, but one is inverted making it convenient for testing the temperature of liquids. Kircher explains correctly the movement of the column of water caused by the expansion of the air, and adds the instrument indicates the goodness, the ​mildness, and salubrity of the air in different places, cultivated fields, plains or mountains, as well as the temperature of man in disease. He mentions a thermoscope containing mercury, but does not describe its construction; the text is accompanied by the figure of a thermoscope of which the stem is twisted into a spiral several feet in length. No reference is made to a scale. (Magnes, 1643, p. 515).
John Baptist van Helmont, a physician and chemist of Brussels, used in 1648 an air-thermometer similar in design to that of Leurechon, except that the stem had only a large drop of water, as in that of Mersenne. (Opera, 1648, p. 64.)
A most important and radical improvement in thermometers was made some time prior to 1654, by Ferdinand II, Grand duke of Tuscany, the liberal patron of literature and art, who devoted himself also to practical researches in physical science. Ferdinand made a thermometer of the usual form, filled it to a certain height with colored alcohol and then sealed it hermetically by melting the glass tip; the ​closed instrument was then graduated by degrees marked on the stem.
This was the first thermometer independent of atmospheric pressure. Torricelli, it will be remembered, had shortly before invented the barometer and demonstrated the weight of the atmosphere. Tuscan savants and Blaise Pascal had applied it to the measurement of elevations. In constructing this new thermometer Ferdinand probably was guided by an experiment made by certain Florentine savants to show the influence of atmospheric pressure. The latter took a U-shaped glass tube open at both ends, on one arm of which two bulbs were blown, the uppermost ending in a very small open point; at the foot of a high tower the U-tube was filled to a certain point with liquid that reached the same height in both arms, and the open point was then closed by melting the glass, care being taken not to warm the air in the bulbs. The whole apparatus was then taken to the top of the tower and the liquid was seen to rise in the open arm and to sink in the closed arm owing to diminished pressure.
Ferdinand also applied the principle of the Cartesian divers to the construction of a thermometer, devising an entertaining apparatus ​(glass bulbs floating in a vessel of water), that puzzled many philosophers; in 1649 he sent one of these to Athanasius Kircher and one to Raphael Magiotti at Rome, with a challenge to explain the paradox, and both the Roman scientists published correct solutions. These instruments, of both the closed and the open forms, found many imitators, Guericke, Kircher, Dalencé, and Pasumot, but are not sufficiently accurate for thermometrical purposes.
In 1657 Ferdinand II, of Tuscany, and his brother, Prince Leopold de Medici, made a most valuable contribution to physical science in promoting the establishment in Florence of a society destined to become famous. The Accademia del Cimento, as its name indicates, was founded for the express purpose of ascertaining by experiment the facts and laws of nature; it numbered only nine members, most of them pupils of Galileo (who had died in 1642), besides a few foreign correspondents, and they devoted themselves to experimental research for truth's sake, taking as their motto "Provando e Riprovando." They did not even seek personal renown, for the results of their investigations were published in the name of the academy only, no individual being ​mentioned. The meetings were held in
* Florentine thermometer.
the palace of Prince Leopold, who also presided. The ecclesiastical authorities did not, however, approve of the enterprise, and the same power that persecuted Galileo caused the academy to be dissolved after ten years of useful activity.
The results or the members' joint researches were published in 1667 in a volume fascinating to the historian of science; the "Saggi di naturali esperienze fatte nell' Accademia del Cimento," which was translated into Latin and into English, the latter by Richard Waller, F.R.S., and published at London in 1684; this edition is the one used in these chapters.
Five instruments for measuring heat were described by the academy:
I. The first is described as a long tube having a spherical bulb and closed with "Hermes' seal" at the flame of a lamp. The tube is filled with "spirit of wine up to a certain mark on the neck, so that the simple cold of ​snow or ice externally applied may not be able to condense it below the 20 degrees of the tube, nor on the contrary the greatest vigor of the sun's rays at midsummer to rarefy it above 80 degrees." The tube is divided into ten equal parts with compasses, each degree being marked with white enamel, and the ten intermediate divisions with green glass or black enamel. The academy preferred alcohol to water because it is "sooner sensible of the least change of heat and cold," and does not freeze in extreme cold. The alcohol is colored with solution of kermes, or of sanguis draconis.
II. The second instrument is "but a copy of the former in little"; the first being divided into 100 degrees and the second into 50. This comparison is then made:
| | No. 1. Degrees. | No. 2. Degrees. |
| Greatest cold of winter | 17 or 18 | 12 or 11 |
| Excessive cold one year | 8 | 6 |
| Midday sun | 80 | 40 |
III. The third thermometer is like the first but much larger, its length being 200 degrees. 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."
V. The fifth instrument was a wide tube of glass nearly filled with spirit of wine in which floated several little glass bulbs adjusted so as to sink to different points in the tube, as the temperature of the liquid rose. This instrument is evidently the same as that of Ferdinand previously noticed.
Although the "Saggi" of the academy were not published until 1667, there is abundant proof that many of the experiments and instruments therein described were devised many years earlier, some of them even before the birth of the academy. It is certain that the principles on which the thermometers were constructed were known in Florence as early as 1641, sixteen years before the academy was founded, and it is highly probable that thermometers Nos. 1 and 2 were made from the ​designs of the Grand Duke Ferdinand himself, for he used them in 1644 when he was experimenting on the artificial hatching of eggs, and in meteorological observations. In 1646 Torricelli showed thermometers of this construction to the distinguished French traveler, Monconys.
The members of the academy used these thermometers, especially the one of 50 degrees which they found the most convenient and accurate, in a variety of experiments with freezing-mixtures and the reflection of cold by a concave glass. The thermometer scales can be thus compared:
Academy thermometers. :
| No. 1 | No. 2. | Fahrenheit. |
| 73 | 37.5 | 96 |
| 49 | 13.5 | 32 |
| −8 | −8.5 | 0 |
In the year 1829 a number of Florentine thermometers were found in a shop in Florence by Antinori, and Libri ascertained their scales to have the following values: (Ann. chim., 45, 354).
| Flor. | C. | Fahr. |
| 13.5 | 0 | 32 |
| 0 | 18.7 | 65.6 |
| 50 | 55 | 131. |
The academy's thermometers were a great ​advance on the baro-thermoscopes that had preceded them, but their graduation left much to be desired; those of different lengths had degrees of unequal value, and individual instruments of the same pattern gave results only approximately similar. Their agreement depended on the skill of the workmen, who sought to get comparable thermometers by taking care to get tubes and bulbs equal in size, but they had no standard of graduation.
Florentine thermometers, made by skilful workmen, became famous throughout Europe; together with Torricelli's barometer and Ferdinand II's hygrometer, they were used at meteorological stations established by the Grand Duke, and conducted in Florence by Raineri, in Pisa by Borelli, as well as in Bologna, Parma, Milan, Warsaw, and Innsbruck; the instruments were observed several times daily and records were kept with great fidelity. One of the Italian day-books containing sixteen years' observations was examined by Libri in 1830, and he obtained evidence that the climate of Tuscany had not materially changed.
The meteorological observations made in Florence from December 15, 1654, to March 31, 1670, were published entire in the ​"Archivio Meteorologico Centrale Italiano," Firenze, 1858, introduction.
The thermometers were introduced into France by the way of Poland; the Grand Duke Ferdinand presented some philosophical apparatus to the Envoy of the Queen of Poland, and her secretary sent one of the thermometers to the astronomer Ismael Boulliau in Paris, with the statement that Ferdinand always carried in his pocket a small one about four inches long.
Meteorological observations were carried on in Paris from 1670 with an instrument made for De la Hire by Hubin. The scale was arbitrary, but the thermometer was preserved until those with reliable scales were manufactured, and its values determined by comparison, thus permitting the records to be adjusted.
Florentine thermometers continued to be manufactured for general use in the eighteenth century; G. Reyger records that Hanow, in his observations of the weather in Danzig made in 1741, reported temperatures in degrees of the "usual Florentine scale, the 0 being in the middle of the tube, indicating temperate air, or 45 Fahrenheit." A. Momber also states that many thermometers made in Danzig as ​late as the middle of the eighteenth century had three scales, Réaumur, Fahrenheit, and Florentine; one of these is in the possession of the Naturforschende Gesellschaft of Danzig. Réaumur, writing in 1730, speaks of Florentine thermometers as in common use.