|Speaker:||Robert Soulen, Naval Research Laboratory|
|Topic:||“A Thermometric Odyssey”|
President Haapala called the 2156th meeting of the Philosophical Society to order at 8:18 p.m. on January 24, 2003. The Recording Secretary read the minutes of the 2154rd meeting and they were approved as read.
The speaker for the 2156th meeting was Robert Soulen, currently a Staff Physicist of the Naval Research Laboratory. Previously he worked at the National Institute of Standards and Technology, until 1987. The title of his presentation was “A Thermometric Odyssey”. The speaker dedicated this talk to his mentor at NIST, Ralph Hudson.
Early marketing strategies for Shredded Wheat cereal included cards of outdoor lore presented by the mythical “Straight Arrow”. These bits of interesting fact included the observation that one could tell the temperature of the environment by counting the rate of “chirps” made by crickets. The speaker, then a youngster in the wilds of New Jersey, was determined to find it this were true, and if so how the crickets knew the temperature. He learned that only the male crickets make the chirp sound by stridulations with their hind legs and that this is related to attracting a mate. Mr. Soulen collected crickets and measured the rate of their chirps as a function of temperature which formed an impressive linear relationship. Was there a local dialect or did regional variations exist in the cricket's chirp rate at a fixed temperature, Mr. Soulen wondered. He then presented data showing that several species of crickets do have a linear relationship between chirp rate and temperature, but that the slopes of these functions was different from species to species. However no detectable dialects were found between different locations for the same species.
Mr. Soulen then addressed the establishment of limits on the temperature scale. Current conventional wisdom holds that the lowest point of the temperature scale is absolute zero a temperature which has almost been reached in the laboratory. Using Helium temperatures in the nano-Kelvin range have been recorded. No certain upper limit has been agreed upon. He noted that the steel industry works in the 2,000 K range while particle accelerators have achieved 1015 K. Calculations of temperatures of the Universe within milliseconds of the Big Bang indicate that the Universe was at a temperature of 1035 K. Mr. Soulen indicated that this temperature was close to the maximum of the temperature scale. In theory 40 orders of magnitude were achievable but that 1 K to 104 K is the working range of modern Physics.
Our basic notion of the temperature scale came from the Greeks. Establish two fixed points and then subdivide the difference into arbitrary units. For the cold point they used snow at altitude on a particular mountain and for the warm point, the armpit temperature of a human. There was no evidence of attempt to calibrate the human. The Mediche family in Italy during the 1600s became the leader in Europe in the making of thermometers. They used sealed glass tubes drawing on the abundance of skilled glass makers in the region. The speaker provided illustrations of some of these elegant spiral creations some of which appeared to use alcohol as a working fluid, also in abundance locally.
Daniel Gabriel Fahrenheit was born to a Polish shipping family. He trained in medicine but was eventually sent into the business world to aid the family business. His interests and talents lay in other areas beside shipping and trade and he was forced to flee Holland to avoid arrest for some business practices presaging Enron. He became an instrument maker noted for the highly accurate bore of the glass tubes used for thermometry. He established two fixed points, then subdivided the interval into the scale which is still used today in tradition bound societies such as the U.S.
The next notable advances in thermometry mentioned by the speaker were produced by William Thompson also known as Lord Kelvin, named after the River Kelvin in Scotland. A precocious individual from a learned family, Thompson graduated from Glasgow University at age 10 and graduated at age 16 from Cambridge. Thompson did early calculations of the impedance of wire which was important to the successful implementation of the transatlantic cable. Another application of thermometry to occupy Thompson was the calculation of the maximum power which could be derived from the steam engine and proved that the maximum power was determined by the ratio of the maximum and minimum temperature of the working fluid. The link between temperature and energy led to the calculation of Absolute zero. This is used at one calibration point of the modern temperature scale by the former National Bureau of Standards, now NIST. The other calibration temperature is the triple point of water. NIST now uses physical laws to calibrate instruments. The international temperature scales left the region below 1 K uncharted but this has now been accomplished by NIST.
The focus of Mr. Soulen's research has been on this region. The results of the speaker's research on establishing the temperature scale below 1 K were recently incorporated into the internationally sanctioned temperature scale extending from 0.001 K to 1 K. Mr. Soulen noted there are some interesting physics in the Helium 3 transition, which helps to account for the 15 % variation in international experimental results reported in the literature. Temperature measurements in this region employ the observation that voltage fluctuations in resistors decrease linearly with decrease in temperature. These voltage fluctations are converted to frequency signals for ease of recording. Researchers Colewell and Fogle are currently working on the development of instrumentation for temperature measurements in the below 1 K range while a laboratory in Berlin, Germany is providing collaboration. The speaker closed his remarks with the observation that “A person with one thermometer always knows the temperature, that person with two thermometers is never sure.”
The Society thanked the speaker who then took questions from the floor:
Q- How can you use a resistor to measure these very low temperatures? What about the heating of the resistor?
A- Heating is not a problem. Only a voltage is applied, there is no current.
Q- What about the cricket thermometers?
A- Katydids also show a linear temperature dependant chirp rate but the slope of the temperature/frequency function is different from crickets. Mathematical simulation indicates that there is an exponential function hidden in the data. It only looks linear due to the short range of experimental temperatures. Working with crickets presents some unexpected difficulties for researchers used to working in physics. In the speaker's experimental setup, the cannibalistic behavior of crickets was expressed when the Bass ate the Soprano.
Q- How close to absolute zero can one get?
A- To date 10-9 has been obtained. To get closer will depend on the extent of future funding.
Q- Are any laboratories making calibrations in the milli-Kelvin range?
Q- What is the triple point you referred to?
A- Very pure water gives a temperature of 100 micro Kelvin at the triple point, a fixed point temperature and pressure.
President Haapala then thanked the speaker again for the society and presented him with a framed, signed copy of the lecture abstract, made the standard announcements and requested that all members of the Society who were present take home a copy of the collected lecture notes from the previous year in order to spare the Society the additional cost of postage. Only paid members receive the collected lecture notes. He then adjourned the 2156th meeting to the social hour at 9:30 p.m.
|Temperature:||-4.4°C (268.7 K)|
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