Many of the difficulties people have in understanding physics can be traced to its language. Not only are the scientific meanings of such terms as "mass," "heat" and "temperature" different from their everyday ones, but these scientific meanings become clear only from the rather specialized context in which they are used.

A case in point is the word "temperature." Physicists usually define temperature, very roughly, as a measure of the average kinetic energy (or energy of motion) of the atoms that make up matter. This definition, however, is at odds with the common notion that temperature is a measure of heat. Heat added to or withdrawn from a substance will in many cases not affect the movements of the atoms of the substance which influence its temperature, but only those chemical and electrical forces that determine whether the substance is a gas, liquid or solid. When ice is melted and turned into ice-water, for example, it undergoes no change in temperature. Temperature and heat must in general be sharply distinguished; the former is a property of matter, the latter is a type of energy that flows from one system to another due to a temperature difference between the two.

All of which might elicit feelings in the layman from indignation to despair -- indignation that there should be such a wide gap between the scientific and everyday meanings of even very basic terms, despair that he will ever be able to cross this gap. For anyone who would nonetheless like to try. David Wilson's "The Colder the Better" will be a substantial language aid. A rigorous introduction to the science and technology of extremely low temperatures (which is called cryogenics), the book constitutes a kind of adult education course in physics for advanced laymen. Ranging over topics, from the cooling and freezing produced in ancient civilizations to the incredible phenomena of superconductivity and superfluidity discovered in this century, "The Colder the Better" is popular scientific writing at its most reliable and authoritative. Wilson has a background in both physics and history, and his familiarity with the scientific aspects of his subject is equaled by his knowledge of the social and historical factors that have influenced its development. Written in an uncondescending, lucid style, his book will give the interested reader, if not complete literacy in low temperature physics, then at least a working vocabulary.

Among the many topics Wilson discusses, that of "superfluidity" is especially interesting. This term refers to the ability of liquid helium, when lowered to temperatures of 2.2 degrees above absolute zero to undergo certain remarkable changes in its properties, including a sudden, million-fold increase in heat conductivity and an almost complete loss of viscosity or resistance to flow. Wilson, whose tone is normally restrained, describes liquid helium's loss of viscosity this way: "half filling a small glass beaker . . . [the fluid] will actually climb up the sides of the beaker, move over the top lip . . . and drip steadily into the pool of liquid below. To say that nothing like this had even been seen before is to understate the case -- it is a complete denial of everything that we all associate with the normal state of matter."

To date, no generally acceptable theory for the phenomenon of superfluidity has been developed. However, the physicist Kurt Mendelssohn, in his book, "The Quest for Absolute Zero" maintains that superfluids are best understood as highly ordered states of matter analogous to crystalline solids, but with their "order pattern" consisting in a "state of motion" rather than "the normal behavior of matter," Mendelssohn suggests that such a perspective may be -- like so many of our "everyday" viewpoints -- absurdly parochial. "In fact, he says, in extra-terrestrial conditions, superfluidity may be the norm. And Wilson's "normal state" of matter "may turn out to be a rare and quaint exception confined to highly unrepresentative conditions, such as the surface of this planet."