Famous People

D aniel Bernoulli (1700 – 1782)

Daniel Bernoulli was a Dutch-born mathematician who spent much of his life in Switzerland. He was born into a family of leading mathematicians but also into a family where there was unfortunate rivalry, jealousy and bitterness. Daniel won the annual prize of the French Academy ten times for work on vibrating strings, ocean tides, and the kinetic theory of gases. For one of these victories, he was ejected from his jealous father's house, as his father had also submitted an entry for the prize. Daniel had also attained fame through his work Mathematical exercises after which he was invited to take up the chair of mathematics at St Petersburg. His brother Nicolaus(II) Bernoulli was also offered a chair of mathematics at St Petersburg so in late 1725 the two brothers travelled to Russia. Undoubtedly the most important work which Daniel Bernoulli did while in St Petersburg was his work on hydrodynamics. His book entitled Hydrodynamica is regarded as the first book on fluid mechanics. This work contains for the first time the correct analysis of water flowing from a hole in a container. This is based on the principle of conservation of energy. Hydrodynamica also contains the development of a kinetic theory of gases, His kinetic theory proposed that the properties of a gas could be explained by the motions of its particles. Daniel also discussed pumps and other machines to raise water.

Supplementary texts Part I What do the words ‘Hot’, ‘Cold’ , and ‘Temperature’ mean?

The words “hot”, “cold”, and “temperature” are associated in our minds with the subject of heat, most of our ideas about hot or cold resulting from our everyday experiences with heated or cooled objects. However, “hot” and “cold” are very general terms.

Calling a summer day “extremely hot” is an ordinary thing with us. We generally forget that the actual temperature is certainly not so high as that which is caused by a “hot fire” in a fireplace. Furthermore, what is hot to one person may be cool to another. As an example, consider the case of two men; one of them is a fireman on a locomotive and the other — a worker in a cold-storage plant. The surroundings of the locomotive fireman are certainly hot, the temperature greatly exceeding that of a hot summer day. Thus, on leaving the locomotive firemen will find that the warm summer evening is rather cool.

On the other hand, when the worker of the cold-storage plant stops working and leaves his cold surroundings, he may find that very evening extremely hot.

If you have ever entered the cellar of a large building after being out on a hot summer day. you have probably thought the cellar a very cool place. On the other hand, if you re-enter that same cellar after being out on a cold day in winter, you will find that the temperature in the cellar is much warmer than that in the street. The actual temperature in such a cellar probably does not vary more than a few degrees from summer to winter but it seems “cool” at one time and “warm” at another, as we have already seen, our temperature sensations arc unreliable, indeed.

Besides their being often used in everyday speech, the words “hot”, “cold”, “temperature” are also basic terms that are scientifically defined when heat is studied. Here, as in many other cases in science, it is necessary to remember that the scientist must define his terms and the phenomena studied with great precision.

The temperature of a body is not a measure of the quantity of energy that this body contains, as some people think. It is, rather, a measure of the molecular motion intensity. For a given object, the temperature is proportional rather than equal to this amount of energy.