At the conclusion of his famed 1865 paper announcing the discovery of a new property of matter that he named entropy, Rudolf Clausius stated: the entropy of the universe tends to a maximum. This statement came as a total surprise to me as there was no prior supportive discussion behind it, and it had me wondering whether or not Clausius truly understood its meaning. Fortunately for us, someone else did understand its meaning as manifested by the fact that this person evolved this statement into one more critically relevant to thermodynamics: the entropy of an isolated system increases to a maximum. The person? J. Willard Gibbs. To understand how this came about, check out this video.
I go into much more depth on the combined work of Clausius and Gibbs in my book Block by Block – The Historical and Theoretical Foundations of Thermodynamics.
Identifying the Micro behind the Macro 