BRIEF BIOGRAPHIES OF
COUNT RUMFORD AND JAMES JOULE

As you will have heard many times before, Galileo had many, varied scientific interests. One that I have not mentioned previously is his invention of the first practical thermometer; the first instrument for actually measuring temperature appears to have been invented by Galileo some time around 1600. However, there were a number of interesting, even bizarre, ideas and developments associated with the measurement of temperature that a short historical description seems entirely appropriate. The first mention of a device resembling a thermometer was by Philo of Byzantium (2nd century BC) although he was actually more interested in studying the properties of air and water. He connected a tube to a globe containing air and dipped the other end under water. When he heated the globe the air expanded and was expelled, and when he cooled the globe the air contracted and water was drawn up the tube. The association of some change in physical property with temperature, for example, as in Philo's experiment the expansion of a gas, is an essential principle underlying all temperature measurements but for centuries the only 'thermometer' continued to be the senses. Some quantification of hot and cold in numerical degrees was done by Galen (129-200 AD). He suggested a 'neutral heat' that was neither hot nor cold - actually an equal mixture of ice and boiling water, which he considered the coldest and hottest possible substances, respectively - as a zero point. So someone of hotter temperature would consider the neutral temperature 'cold' and someone of colder temperature would consider it hot. From these ideas Arab and Latin physicians developed scales of degrees, the most popular being one that ranged from 0 to 4 degrees of heat. Drugs, for treating medical ailments, were supposed to have something analogous to a heating and cooling effect and so were given a place on the scale. Other scales - one of 8 degrees - were adopted also so by the 16th century, though the senses were the only means of estimating temperature, the concept of 'degrees' was well established.


The first 'proper' thermometers were adapted from Philo's apparatus. The stem was marked in degrees and the movement of water was taken to indicate temperature. They were rather inaccurate because, as we now know, changes in atmospheric pressure would also cause the height of the water to vary! The association of Galileo with this invention lies solely on the accounts of his contemporaries; he does not appear to have written anything about it himself. The first published evidence appeared in 1612 in an article by Santorio Santorii (1561-1636), a professor of medicine at the University of Padua, who had been a pupil of Galileo. Santorio used it to estimate the heat of the heart by measuring the temperature of a patient's breath, which was thought to come from the heart! He also made instruments to measure the temperature in the mouth and the hand. He had introduced, in effect, the first clinical thermometers. Galileo's strong influence on Santorio's approach to physiological problems is also demonstrated by the latter's development of the pulsilogium, a small pendulum device for measuring a patient's pulse rate, as we have already seen.

The idea of temperature or of hotness and coldness is, like length, time and mass, one of the fundamental concepts that describe natural phenomena. So, in order to compare temperatures in different locations, by different people, at different times, a standardized temperature scale was required. The underlying principle of measuring temperature and assigning a scale (and a unit) is that one needs to use some property of a substance (or substances) that depends critically and uniquely on temperature. One of the earliest attempts at developing a scale of temperature was by Newton in 1701. He arranged simple physical processes such as the freezing of water, the melting of wax, the boiling of water, etc. in order and assigned different numerical values to them on two different scales, one arithmetical [1] and the other geometrical [2].

During the 17th and 18th centuries there were many improvements in thermometry, principally by Gabriel Fahrenheit (1686-1736), Ferchault de Reamur (1683-1757) and Anders Celsius (1701-1744). Various liquid thermometers were developed that allowed a definition of fixed points, e.g., the ice- and steam-points, that permitted various temperature scales. For example, we are all acquainted with the Fahrenheit scale; originally, the lowest temperature (0oF) was that reached by a 50% mixture of snow and salt (NaCl) and 100oF was taken as the temperature of the healthy human body. On that scale, the ice-point was 32oF and the steam-point was 212oF - the standards we use today. The Celsius scale, after modification [3] took zero, i.e., 0oC, as the ice-point and 100oC as the steam-point.

The difference between a quantity of heat and temperature, frequently used interchangeably but quite wrong, was cleared up by Joseph Black (1728-1799) who introduced the science of calorimetry. He also developed the idea of the specific heat of a substance and discovered the concept of latent heat in changes of state, i.e, that during the melting of ice (to water) and boiling of water (to steam) large amounts of heat were absorbed without a change in temperature in order to produce the change in state.

However, the nature of heat was not at all well understood. One idea that had a good deal of support was that heat was a fluid, called caloric, made up of small particles that repelled each other but were attracted to matter; the caloric flowed from a hotter to a colder object. Heat from friction was explained as being due to the fact that friction removed some of the caloric and so made the object appear warmer. The melting of ice was explained in terms of the combination of caloric with the ice to form water similar, in a way, to a chemical reaction. Black was a supporter of the caloric theory although a number of earlier scientists, like Newton and Robert Boyle, thought that heat was related to the motions of the particles in bodies.


At the end of the 18th century, Benjamin Thompson (1753-1814), later Count Rumford [4], conducted a series of studies that later appeared to have been very convincing experiments on the nature of heat. In correspondence he says:

He poses the question:

He took samples of the chips produced during the boring and also the same weight of small test pieces of the barrel material, heated them in boiling water and then transferred them into equal amounts of cold water (at 59.5oF) to test whether the "... capacity for heat ..." had been reduced by the borer. He repeated the experiment several times but found that results were always "... so nearly the same ...". He concludes:

Rumford's experiments were pretty much disregarded until the middle of the 19th century when two independent developments took place that led to a general acceptance of the mechanical theory of heat. The first was due to Julius Mayer (1814-1878) in 1842 that heat and work were equivalent and could be converted from one to the other [5]. The second was by James Prescott Joule (1818-1889) who actually measured the equivalence between work and heat (as we will see below).

Joule was born near Manchester, England on December 24, 1818, the son of a prosperous brewery owner. It was the period of the first Industrial Revolution and the growing use of labor saving devices was causing serious problems in the supply of labor and the factories in Manchester were particularly notorious for the appalling conditions that workers had to experience. The cultural atmosphere was as stifling as the bad air from the factories and the confined housing of the factory workers. It was in this environment that Joule spent most of his life.


He was educated at home by tutors until at age 16 when, together with his brother, he was sent to study under the chemist John Dalton (1766-1844) for a short time. The contact with Dalton stimulated his interest in science but because he was of independent means Joule sought limited formal training; his interest in science was a form of entertainment for him. In 1838 he converted one of the rooms at his father's house into a laboratory and he started his experimental investigations. Later in 1838 he published his first scientific paper but his first, real contribution was not until he presented a paper to the Royal Society in 1840 [6], in which he showed that the rate at which heat is produced by an electrical current in a conductor is proportional to the square of the current, i.e.,

H ~ I2Rt

where I is the current, R is the resistance of the load (heater) and t is the time. For the next ten years Joule carried on his studies of heat, continually refining his approach and reporting his progress to the Royal Society.

His work on the mechanical equivalent of heat was reported first in a letter to the editor of the Philosophical Magazine in 1845 [7], and in 1850 he presented a memoir in the Philosophical Transactions of the Royal Society [8] that contained his most precise value of the mechanical equivalent of heat, deduced from his famous paddle-wheel experiment. After presenting the paper he was elected a Fellow of the Royal Society. The apparatus he used is shown below:



and extracts of the theory are described in figure 1 and figure 2.

After 1850, his researches, while numerous and significant, did not qualify as important as his work on the mechanical equivalent of heat. He carried out experiments with William Thomson (1824-1907) [9] on the cooling effect of an expanding gas [10]. Towards the end of his life he was overcome by economic misfortune and his income was not sufficient for him to continue research at his own expense. In 1878 he obtained a pension from the Government, which contained until his death in 1889. The most prestigious honor he received was that conferred by the second International Congress to use his name for the unit of energy.

FOOTNOTES

[1] An arithmetical scale is linear with a constant spacing, e.g., 0, 2, 4, 6, 8 ... when the next number in the sequence is generated by adding a constant number (2 in this example) to the previous one.

[2] An example of a geometrical scale is 1, 3, 9, 27, 81 ... when the next number in the sequence is obtained by multiplying the previous one by a constant number (3 in this example).

[3] Celsius originally suggested that the boiling-point of water be zero degrees and the ice-point be 100 degrees but his colleague, Marten Strömer, inverted the scale to produce the one we are familiar with today.

[4] Thompson was an American born in Woburn, Massachusetts. During the Revolutionary War he was loyal to the British Crown and left the USA for Britain in 1776. He settled in Bavaria, won the friendship of the Duke and was made a Count of the Holy Roman Empire and served as minister of war. Although scientific historians tend to refer only to his work on the nature of heat, his interests were very wide spread. He wrote papers on the improvements to fireplaces (1796-8), developing what is now known as the 'Rumford fireplace', and was interested, among other things, in central heating, the kitchen oven, thermal underwear and the pressure cooker.

[5] This was essentially the principle of the conservation of energy ... "that energy can neither be created nor destroyed but can be converted from one form to another".

[6] Philosophical Magazine, 19, 260 (1841).

[7] "On the Existence of an Equivalent Relation between Heat and the Ordinary Forms of Mechanical Power" Philosophical Magazine, 27, 205 (1845).

[8] Philosophical Transactions of the Royal Society, 140, 61 (1850).

[9] Later Lord Kelvin.

[10] The so-called Joule-Kelvin effect is used in the liquefaction of helium.

REFERENCES

Books

M. Shamos Great Experiments in Physics (Dover Publications Inc., New York, 1987).

Web-sites