# Bernoulli succeeded despite paternal rivalry

Imagine having your father ban you from his house when he couldn't bear being compared as your equal, and then plagiarizing your work. Such was the life of Daniel Bernoulli (1700-1782), the Swiss mathematician and physicist.

Coming from a notable family of mathematicians, Bernoulli distinguished himself at a young age as being one of the brightest. His father, Johann, was head of mathematics at Groningen University in the Netherlands (before they moved to Basel, Switzerland) and made important contributions to calculus. His uncle Jacob Bernoulli did early work in probability theory.

As a child, Daniel's father wanted him to be a merchant, then wanted him to him study medicine, which he did — all the while being tutored in math by his father. When Daniel was just 25 years old, Empress Catherine I of Russia invited him to become a professor of mathematics at the Imperial Academy in St. Petersburg. His brother Nikolas accompanied him, but when Nikolas died of tuberculosis a year later, he was replaced by a scientist by the name of Leonhard Euler. With Euler, Bernoulli studied flow dynamics, particularly in relation to blood.

Daniel developed a method to test blood pressure. For almost 200 years, physicians in Europe used Bernoulli's method of testing pressure by sticking a pointed glass tube straight into a patient's artery to see how high the blood rose in the tube.

Bernoulli's principle of fluid dynamics states that an increase in a fluid's speed occurs simultaneously with a decrease in pressure. Fortunately no longer used as a method of determining blood pressure, Bernoulli's method is used in aircraft today to measure air speed. A pitot tube mounted on the wing of an airplane determines the stagnation pressure of the air flow, while a static port, a tube with holes on the sides, measures the static pressure, which is the pressure created by the moving airflow. The difference between the two determines the dynamic pressure, which indicates the plane's air speed, as shown on the air speed indicator.

Bernoulli's principle is also often used as a simplistic explanation of how a plane flies — because the top of an airplane's wing is curved while the bottom is flat, air travels slower on the bottom (creating more pressure) and faster on the top (creating less pressure), which creates lift, keeping the aircraft in flight.

When Daniel was 34, he and his father jointly won a prize by the French Academy of Sciences. Johann, not wanting to admit that his son was his equal, banned Daniel from his house.

Daniel published his greatest work, *Hydrodynamica*, in 1738. In it, he stated his principle of fluid dynamics and laid the basis for the kinetic theory of gases. His father published a similar book, *Hydraulica,* a year later with many of the same ideas as Daniel's, but backdated his book to appear as if it were published first.

Daniel tried to reconcile with his father, but Johann refused. Eventually, Daniel turned his pursuits to medicine and physiology, leaving the mathematics to his father.

Daniel Bernoulli died in Basel, Switzerland on March 17, 1782 at the age of 82; but the principles he discovered have assured him a place in history where his work still lives.