073

The Hunterian Museum, Glasgow, Scotland

55° 52′ 19″ N, 4° 17′ 19″ W

William Hunter and Lord Kelvin

The 18th-century anatomist and obstetrician William Hunter (brother of John Hunter; see Chapter 64) bequeathed the money for the creation of the Hunterian Museum in Glasgow. He also provided the core of its collection—his medical equipment and specimens, and his wide-ranging collection of art works, coins, books, and minerals. In the 200 years since its creation, the museum has vastly expanded its collection of scientific and artistic works, and also contains the most important public exhibition of the work of another great Glaswegian, William Thomson (who became Lord Kelvin).

William Hunter introduced the practice of using cadavers to teach medical students. He eventually specialized in obstetrics, publishing his illustrated The Anatomy of the Human Gravid Uterus in 1774 (see Figure 73-1).

Figure 73-1. Illustration from The Anatomy of the Human Gravid Uterus

The museum celebrates Hunter’s life through his collection, with a special emphasis for scientists on his medical equipment and pathological specimens. The collection also includes early X-ray and ultrasound equipment. The most up-to-date part of the exhibition examines the MRSA (multiple-resistant Staphylococcus aureus) bacterium, which is hard to treat because of its drug resistance, and the Glasgow Coma Scale (a scale of 3 to 15 indicating the degree of responsiveness of a coma patient).

William Thomson was born in Belfast, and came to Glasgow when his father was appointed professor of mathematics at the University. Thomson went on to Cambridge University and a spectacular career that spanned both theoretical and practical work. The Hunterian Museum describes him as the greatest Glaswegian scientist, which is undoubtedly true, but his impact was felt far from Glasgow and to this day.

Lord Kelvin’s practical inventions included the mirror galvanometer, which extended the telegraph to all parts of the British Empire (see page 236). Kelvin also gave his name to the standard unit of temperature (see sidebar), coined the term “kinetic energy,” built a highly accurate machine for predicting tides, and was a mentor for James Clerk Maxwell (see Chapter 35). He stands among the world’s greatest scientists, along with Newton, Einstein, and Faraday. He is buried in Westminster Abbey next to Newton.

One of Kelvin’s often-overlooked inventions is his compass (Figure 73-3). In 1874, he wrote and lectured extensively about magnetic compasses, the Magnetic North Pole (see Chapter 128), and problems with navigation. His compass was both very sensitive and able to cope with the ravages of a moving ship at sea, and it could be tuned to eliminate magnetic deviation caused by the use of iron in the ship’s construction. That was achieved by the placement of a small magnet close to the compass to eliminate the ship’s magnetic field.

The museum’s special Kelvin exhibition contains his original equipment and a range of hands-on experiments ideal for schoolchildren. Apart from an oddly fearsome-looking Kelvin dummy, which seems a little out of place, the exhibition does a good job of explaining Kelvin’s theoretical and practical work.

The museum also makes use of multimedia to add depth to Kelvin’s life, and offers the ability to further explore the museum’s collection of Kelvin’s equipment, and computer-based animations explaining his work.

Figure 73-3. Kelvin’s compass; courtesy of Don Turnbull (http://donturn.com)

Practical Information

The Hunterian Museum’s website is at http://www.hunterian.gla.ac.uk/. Admission is free. A useful online resource for Kelvin research is Scran (http://www.scran.ac.uk/), a fully searchable database of items held in Scottish museums—just do a search for “lord kelvin”.

Measuring Temperature

Lord Kelvin’s name is so well known partly because it is used as the standard international unit of temperature, the kelvin. For most scientific work, the kelvin has displaced Celsius and Fahrenheit.

The Fahrenheit scale was proposed in 1724 by the German physicist Daniel Gabriel Fahrenheit. His scale was developed, at least in one telling of the story, by fixing three interesting points: 0°F, 32°F, and 96°F. Fahrenheit set 0°F as the temperature of a mixture of water, ice, and ammonium chloride. This curious mixture was actually a common way of getting a fixed, low temperature at the time, since the mixture will automatically find and stay at a specific temperature.

32°F was the temperature of water with ice melting in it, and 96°F was the temperature of a healthy person taken under the arm. Later recalibration of the scale led to the standard healthy human temperature being 98.6°F.

Around 1742, the Swede Anders Celsius proposed a different scale, where 100°C was the freezing point of water and 0°C the boiling point of water. He was careful to point out that the boiling point of water is affected by air pressure, and that fixing 0°C should be done at mean pressure at mean sea level. Not long afterward, the scale was reversed to form the familiar Celsius scale used today.

In 1848, Lord Kelvin wrote the paper On an Absolute Thermometric Scale and proposed a radically different way of looking at temperature based on the actual nature of temperature itself. Kelvin’s paper proposed that a temperature scale be based on the lowest temperature possible (the infinitely cold); today we call this Absolute Zero.

Temperature arises from the motion of particles. For example, the temperature of the air arises from the random motion of air molecules—the higher the temperature, the faster the molecules move about and bounce off each other. Absolute Zero is the temperature at which motion is at a minimum and can go no lower.

In defining his unit of temperature, Kelvin used Absolute Zero as the zero value and the same degrees as Celsius. He calculated Absolute Zero to be –273ºC; today, the accepted value is –273.15ºC. Thus the freezing point of water is 273.15 K and the boiling point is 373.15 K.

In accurately defining the kelvin scale, today two values are used—Absolute Zero and the triple point of Vienna Standard Mean Ocean Water. The official definition is that the kelvin “is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.”

The triple point of water (Figure 73-2) is a specific temperature and pressure at which all three forms of water (liquid, solid, and gas) coexist. This occurs at 273.16 K (0.01ºC) with a pressure of 611.73 pascals. At that temperature and pressure, it is possible to cause all the water to turn into any one of the forms (liquid, ice, or vapor) by changing the pressure or temperature.

Figure 73-2. The triple point

Of course, the actual composition of the water makes a difference to its triple point, thus the specification of Vienna Standard Mean Ocean Water (VSMOR). The VSMOR is a precise definition of the composition of pure water that specifies the proportions in which isotopes of hydrogen and oxygen are found (and is intended to reflect real average ocean water). Despite the “ocean” in its name, the water is pure—there are no salts or minerals present.

Because the triple point of water is fixed, it is commonly used as a calibration point for thermometers. This is achieved by placing the thermometer inside a triple point cell—an enclosed tube nearly filled with water, leaving a gap containing just water vapor.

The cell contains a slot for the insertion of a thermometer. To get the water to the triple point, the entire cell is cooled down to near freezing. Then dry ice is placed in the thermometer slot, which causes the water around the slot to freeze. Once this mantle of ice extends for a few millimeters, the dry ice is removed and a warm metal probe briefly inserted in the slot. The ice mantle melts slightly and floats off into the water. At that point, water, ice, and vapor are all present in the tube, and it can be used to calibrate a thermometer very precisely.