In the fields of observation chance favors only the prepared mind – Louis Pasteur [1]

The piston played a critical role in the history of thermodynamics as this device, embedded within the steam engine, transformed heat (Q) generated by a steam boiler into the work (W) required to lift buckets of water out of deep mines. Rudolf Clausius quantified this law in 1850 by conducting an energy balance around the piston. He stated 1) that U, a new thermodynamic term he created that later became known as internal energy, is a conserved property of matter, and 2) that the U of the working substance inside the piston only changes if heat (Q) is added to the system or work (W) is done by the system. If no Q and no W, then ∆U is zero.

∆U  = Q – W

Clausius based his work on Sadi Carnot’s groundbreaking theoretical analysis of the steam engine and also on the independent findings of two men, Julius Robert Mayer (1814-1878) and James Joule (1818-1889), neither of whom held an academic position. Mayer (1842) and Joule (1849) both demonstrated, for the first time in history, the existence of an exact relationship between Q and W that permitted Clausius to include both in the above equation. This relationship, called the mechanical equivalent of heat (MEH), states that the (reversible) fall of a 778 pound weight through one foot of distance increases the temperature of one pound of water one degree Fahrenheit.

Mayer the outsider

Many thought Mayer’s calculation of the mechanical equivalent of heat was a fluke. How could a non-scientist ever be the first to arrive on top of such a profound pinnacle of achievement?  His path was an enigma.  His sources obscure.  He had no pedigree.  Seemingly out of the blue, Mayer arrived at the mechanical equivalent of heat in 1842 and then at a more encompassing theory of energy in 1845.  But Mayer was no fluke.  He was a brilliant thinker who had the simple misfortune of being an outsider.

Born in Heilbronn, Germany, son of an apothecary, Mayer grew up with a fascination in machines.  So strong was this fascination that at one point he attempted to build his own perpetual motion machine.  His failure led to an extremely valuable experience, one that would guide his thinking in later years:  one can’t generate mechanical work out of nothing.

Mayer was neither physicist nor scientist.  He had no obvious strengths in mathematics or natural science.  He was a doctor. But behind this exterior was a deep and original thinker who had an extremely logical mind that adhered to a deep belief in causality as manifested by his oft-spoken slogan, causa aequat effectum (cause equals effect), and as inspired by his childhood failure in building a perpetual motion machine.  And with this mind Mayer went on his own journey, seeking to understand the very simple but profound observation that blood is redder in warmer climates.

The Java

After obtaining his medical degree from Tübingen in 1838, Mayer jumped aboard the Java in 1840 as it sailed from Rotterdam to the Dutch East Indies, earning his passage as the ship’s doctor.  Alone during the trip with much free time on his hands, Mayer occupied himself “zealously and unremittingly with the physiology of the blood.”[2]  He studied hard, thought hard and noticed much.  His mind was prepared for what happened next.

Upon arrival in Indonesia, some of the crew became ill, necessitating the common cure of the day, blood letting.  In Mayer’s own words, “In the copious bloodlettings I performed, the blood let from the vein in the arm had an uncommon redness.” [3]  Out of all the many observations Mayer made, this one stood out.  His education prepared him to notice something as “uncommon” as this.  Venous blood wasn’t supposed to be so red. 

Many ignore the uncommon observation, the outlier, and simply let it float away.  But others pounce on it, grasp it, and pull it apart, seeking the deeper underlying cause.  Mayer was one such person.  There was no plan here, no nice, neat path in front of him.  He could have turned away to another path, but he didn’t, a strong testament to his intense need to understand the cause behind the effect.  Why was the blood so red?

The meaning of bright red blood

When lungs pull in air, oxygen latches on to the hemoglobin in the blood, turning it bright red.  The blood carries the oxygen to the cells through the arteries, where it reacts with the food to generate both cell structure and heat to keep us warm.  This “combustion” process yields carbon dioxide as a product which the now darker-red (oxygen-depleted) blood carries back through the veins to the lungs for release.

Based on his reading of Lavoisier, Mayer knew some aspects of this physiology.  He knew that respiration is a form of combustion.  He also knew that combustion releases heat.  Using his penchant for step-by-step, cause-effect deductive reasoning, Mayer deduced that respiration must release heat and so must be what keeps animals warm.  This may seem obvious to us now, but at that time, many were skeptical of Lavoisier’s theories and thought oxygen’s role was solely to remove waste carbon from the body.  Mayer didn’t align with the consensus, a critical attribute for anyone seeking to create something new.  Instead, he embraced Lavoisier’s theories, understood their importance, and instinctively held them as valid.  He sensed the answer to the redder blood:  in warmer climates, less heat generation is needed to keep warm, so less oxygen is combusted, resulting in a higher oxygen-content in the venous blood, making it redder.

The power of analogy

Drawing on his passion for analogies, Mayer developed a view of the human body as a working machine, perhaps inspired by the widely used organism-as-machine metaphor appearing in the German scientific literature in the early 19^th century.[4] To him, the energy first released by the reaction between food and oxygen is “transformed partly into heat, partly into motion; both taken together naturally again give the measure of the first.” [5]  Thus, suggested Mayer, and this was a HUGE “thus,” since heat and work vary in the daily life of an animal but must otherwise sum to the same fixed number to ensure the impossibility of perpetual motion, there must be a quantitative equivalence between heat and work.  This was one of the first conceptual energy balances conducted around the human body. [6]

The power of solitude

All of this thinking materialized during his voyage.  Like Newton’s time in the country, Bernoulli’s in Russia, and Carnot’s in his small Parisian apartment, Mayer’s time onboard the Java provided him the solitude necessary for deep creative thinking.  A critical outcome was his realization that in order to continue progress, he had to crossover from physiology into the world of physics.  Thus did Mayer become yet another grand discoverer to be enabled by a Galilean stance at the interface between different disciplines.

Learn about Mayer’s calculation and what happened afterward!

To appreciate more about Mayer’s accomplishment, check out Chapter 20 in my book Block by Block – The Historical and Theoretical Foundations of Thermodynamics. The story behind James Joule’s accomplishment is in Chapter 21. Thank you for listening!

[1] Louis Pasteur, Lecture, University of Lille (7 December 1854).

[2] Caneva, Kenneth L. 1993. Robert Mayer and the Conservation of Energy. Princeton, N.J: Princeton University Press, p. 7.

[3] Caneva, 1993, p. 27.

[4] Caneva, 1993, p. 142.

[5] Caneva, 1993, p. 239.

[6] One can sees similarities between Mayer’s thought process and Lavoisier’s experimental heat balance around his guinea pig as recounted in Chapter 15 of my book.