Year: Day to Day Men: February 18
The Pose
The eighteenth of February in 1838 marks the birth date of Austrian-Czech physicist and philosopher Ernst Waldfried Josef Wenzel Mach. Due to his contributions to the physics of shock waves, the ratio of the speed of flow or object to the speed of sound is named the Mach number in his honor.
Born at the village of Brno-Chrlice in South Moravia, a part of the Austrian Empire, Ernst Mach was educated at home by his parents until the age of fourteen. He studied for three years at a secondary school in the city of Kroměříž. In 1855, Mach enrolled at the University of Vienna where he studied physics and medical physiology. In 1860, he received his doctorate in physics under Austrian physicist and mathematician Andreas von Ettingshausen, the first to design an electromagnetic machine which used its electrical induction for power generation.
In 1864, Mach turned down the chairman of surgery position at the University of Salzburg to accept a professorship of mathematics at the University of Graz, the second largest and oldest university in Austria. Two years later, Mach was appointed Professor of Physics at the university. In that position, he continued his work in psychophysics, a field that investigates the relationship between physical stimuli and the sensations and perceptions they produce. In 1867, Mach became the chair of experimental physics at Prague’s Charles-Ferdinand University, a position he held for twenty-eight years before returning to Vienna.
Ernst Mach’s primary contribution to the science of physics were his photographs and descriptions of spark shock waves as well as the later studies of ballistic shock waves. Using the technique of schlieren photography, Mach and his son Ludwig photographed the shadows of the invisible shock waves. Invented in 1864 by German physicist August Toepler, schlieren photography is, essentially, a process of photographing fluid flows by measuring the spatial variations in the intensity of a light source shining on or from behind the target object.
Mach’s initial studies in experimental physics was primarily on the refraction, polarization, diffraction and interference of light in different media and under external influences. Further explorations dealt with supersonic fluid mechanics. In a collaboration with photographer Peter Salcher, Mach presented a 1887 paper on his research that correctly described the sound effects observed during the supersonic motion of a projectile. They confirmed the existence of a shock wave of conical shape with the projectile at the apex. The ratio of the speed of a fluid to the local speed of sound (Vp/Vs) is called the Mach number in honor of his work in the field. This ratio is a critical parameter in the description of high-speed fluid movement in the fields of aerodynamics and hydrodynamics.
Ernst Mach also made many contributions to the fields of psychology and physiology. Among these are his discovery of the oblique effect, the relative deficiency in the perception of oblique contours as compared to vertical or horizontal contours. Mach formed an experiment in which he placed a line to make it appear parallel to an adjoining one. Errors in the observer’s perception occurred least for horizontal or vertical orientations and largest when the lines were set at an incline of forty-five degrees. Mach’s experiment showed a perceptible change in the appearance of an object occurs with a forty-five degree rotation.
Another contribution by Mach to the field of sensory perception was the study of effects caused by the optical illusion known as Mach bands. Through this illusion, he explored the edge detection ability of the human visual system. The Mach bands exaggerate the contrast between edges of slightly differing shades of gray as soon as they touch. From this study, Mach made a distinction between what he called the physiological space, specifically visual, and geometrical space.
Ernst Mach survived a paralytic stroke in 1898. He retired form the University of Vienna three years later and received an appointment to the upper chamber of the Austrian Parliament. In 1913, Mach left Vienna and moved to his son Ludwig’s home in Vaterstetten in Upper Bavaria near Münich. Ernst Mach continued his writing and correspondence until his death in February of 1916 at the age of seventy-eight.