Have you ever experienced that wondrous “Eureka!” moment of insight when you’ve discovered some hidden secret of nature? Archimedes did when he realized that the volume of water displaced is equal to the volume of the body submerged. Kekulé did when discovered benzene’s structure. Hubble did when he discovered that the stars are all moving away from us at speeds that increase with distance. And Rudolf Clausius arguably did when he realized that he could correct Sadi Carnot’s “flawed” masterpiece (here) by replacing the caloric theory of heat with James Joule’s theory of work-heat equivalence (here). Clausius’s 1850 publication on this topic gave us the 1st Law of Thermodynamics. I capture the essence of Clausius’s realization in this video.
Carnot’s original work together with Clausius’s 1850 publication are captured well in this book:
I go into much more depth on Clausius’s 1850 publication in my book Block by Block – The Historical and Theoretical Foundations of Thermodynamics.
Identifying the Micro behind the Macro 