This book details an unprecedented finding in the history of economic thought: the true origin of macroeconomics. This occurred in Spain with the researcher Germán Bernácer (Alicante 1883-1965) and his first book: Sociedad y Felicidad. Un Ensayo de Mecánica Social (Society and Happiness. An Essay on Social Mechanics), published in 1916. Twenty years before the publication of The General Theory of Employment, Interest and Money (1936) by Keynes, Bernácer established the fundamental pillars of macroeconomics. Some of these works came to the attention of Professor Robertson in Cambridge where Keynes worked. Villacís demonstrates the invalidity of the fundamental equation of macroeconomics: savings equal to investment. This book discusses the epistolary relationship of the author, José Villacís, with Professor Robert M. Solow.