THE 



POPULAR SCIENCE 



MONTHLY. 



AUGUST, 1908 



THE HISTORY OF THE CONSERVATION OF ENERGY; 

 THE AGE OF THE EARTH AND SUN 



By Professor FLORIAN CA.JORI 



COLORADO COLLEGE 



IN the small town of Heilbronn, in Wiirtemberg, stands a monument 

 erected to the memory of. the physician, Robert Mayer. It was 

 unveiled in 1892, just fifty years after the publication of Robert 

 Mayer's first essay on the conservation of energy. His career as a 

 scientific discoverer is marked by many pathetic incidents. After the 

 study of medicine he was made sanitary officer on a Dutch vessel, bent 

 for the East Indies. During the long ocean voyage on the slow sail- 

 ing vessel he was left much to himself. He gave his leisure hours to 

 the contemplation of scientific subjects. He had occasion to observe 

 that, in tropical countries, blood taken from the veins of patients looks 

 almost like arterial blood. He concluded that in the tropics less 

 oxidation is necessary than in a cold climate, in order to maintain a 

 uniform bodily temperature. There must be a quantitative relation 

 between the amount of heat generated and the temperature in which 

 we live. In cold, northern climates "more heat must be developed for 

 the maintenance of uniform bodily temperature. During the 219 days 

 between February and September, 1840, spent on the water, Mayer 

 dwelt in close intellectual communion with nature, and she gradually 

 revealed to him one of her most precious secrets. Upon his return to 

 Heilbronn he kept on thinking. A moving body is brought to rest by 

 friction; heat appears. Has the motion disappeared into nothing? 

 Has heat sprung out of nothing? If not, then there must be an 

 equivalence between the heat generated and the motion destroyed. 

 Causa aquat affectum, " Cause is equal to effect/' became his favorite 

 axiom. At first he thought that kinetic energy varied as the velocity. 

 Later he recognized his error and perceived its variance with the square 

 of the velocity. 



On June 16, 1841, he sent an essay embodying his new ideas for 

 vol. Lxxirr. — 7. 



