NATURE 



117 



THURSDAY, DECEMBER 14, 1871 



THE COPLEY MEDALIST OF 1871 



DR. JULIUS ROBERT MAYER was educated for 

 the medical profession. In the summer of 1840, 

 as he himself informs us, he was at Java, and there 

 observed that the venous blood of some of his patients 

 had a singularly bright red colour. The observation 

 riveted his attention ; he reasoned upon it, and came to 

 the conclusion that the brightness of the colour was due 

 to the fact that a less amount of oxidation sufficed to 

 keep up the temperature of the body in a hot climate 

 than in a cold one. The darkness of the venous blood 

 he regarded as the visible sign of the energy of the oxi- 

 dation. 



It would be trivial to remark that accidents such as this, 

 appealing to minds prepared for them, have often led to 

 great discoveries. Mayer's attention was thereby drawn 

 to the whole question of animal heat. Lavoisier had 

 ascribed this heat to the oxidation of the food. One great 

 principle, says Mayer, of the physiological theory of 

 combustion, is that under all circumstances the same 

 amount of fuel yields by its perfect combustion the same 

 amount of heat ; that this law holds good for vital pro- 

 cesses ; and that hence the living body, notwithstanding 

 all its enigmas and wonders, is incompetent to generate 

 heat out of nothing. 



But beyond the power of generating internal heat, the 

 animal organism can also generate heat outside of itself. 

 A blacksmith, for example, by hammenng can heat a nail, 

 and a savage by friction can warm wood to its point of 

 ignition. Now unless we give up the physiological axiom 

 that the living body cannot create heat out of nothing, 

 '• we are driven," says Mayer, "to the conclusion that it is 

 the total heat generated within and without that is to be 

 regarded as the true calorific effect of the matter oxidised 

 in the body." 



From this again he inferred that the heat generated ex- 

 ternally must stand in a fixed relation to the work expended 

 in its production. For, supposing the organic processes to 

 remain the same ; if it were possible, by the mere alteration 

 of the apparatus, to generate different amounts of heat by 

 the same amount of work, it would follow that the oxida- 

 tion of the same amount of material would sometimes 

 yield a less, sometimes a greater, quantity of heat. 

 " Hence," says Mayer, " that a fixed relation subsists 

 between heat and work, is a postulate of the physiological 

 theory of combustion." 



This is the simple and natural account given subse- 

 quently by Mayer himself of the course of thought started 

 by his observation in Java. But the conviction once 

 formed that an unalterable relation subsists between work 

 and heat, it was inevitable that Mayer should seek to 

 express it numerically. It was also inevitable that a mind 

 hke his, having raised itself to clearness on this important 

 point, should push forward to consider the relationship of 

 natural forces generally. At the beginning of 1842 his 

 work had made considerable progress ; but he had become 

 physician to the town of Heilbronn, and the duties of his 

 profession limited the time which he could devote to 

 purely scientific inquiry. He thought it wise, therefore, 



VOL. V. 



to secure himself against accident, and in the spring of 

 1843 wrote to Liebig, asking him to publish in his 

 " Annalen " a brief preliminary notice of the work then 

 accomplished. Liebig did so, and Dr. Mayer's first paper 

 is contained in the May number of the "Annalen" for 

 1842. 



Mayer had reached his conclusions by reflecting on the 

 complex processes of the living body ; but his first step 

 in public was to state definitely the physical principles 

 on which his physiological deductions were to rest. He 

 begins, therefore, with the forces of inorganic nature. 

 He finds in the universe two systems of causes which 

 are not mutually convertible ;— the different kinds of 

 matter, and the different forms of force. The first 

 quality of both he affirms to be indestrnctibilily. A 

 force cannot become nothing, nor can it arise from 

 nothing. Forces are convertible, but not destructible. 

 In the terminology of his time, he then gives clear ex- 

 pression to the ideas of potential and dynamic energy, 

 illustrating his point by a weight resting upon the 

 earth, suspended at a height above the earth, and 

 actually falling to the earth. He next fixes his atten- 

 tion on cases where motion is apparently destroyed 

 without producing other motion ; on the shock of inelastic 

 bodies, for example. Under what form does the vanished 

 motion maintain itself .? Experiment alone, says Mayer, 

 can help us here. He warms water by stirring it ; he 

 refers to the force expended in overcoming friction. Mo- 

 tion in both cases disappears, but heat is generated, and 

 the quantity generated is the equivalent of the motion 

 destroyed. Our locomotives, he observes with extra- 

 ordinary sagacity, may be compared to distilling ap- 

 paratus. The heat beneath the boiler passes into the 

 motion of the train, and it is again deposited as heat 

 in the axles and wheels. 



A numerical solution of the relation between heat and 

 work was what Mayer aimed at, and towards the end of 

 his first paper he makes the attempt. It was known that 

 a definite amount of air, in rising one degree in tempera- 

 ture, can take up two different amounts of heat. If its 

 volume be kept constant, it takes up one amount ; if its 

 pressure be kept constant, it takes up a different amount. 

 These two amounts are called the specific heat under con- 

 stant volume and under constant pressure. The ratio of 

 the first to the second is as i : v\2i. No man, to my 

 knowledge, prior to Dr. Mayer, penetrated the significance 

 of these two numbers. He first saw that the excess o'42i 

 was not, as then universally supposed, heat actually 

 lodged in the gas, but heat which had been actually con- 

 sumed by the gas in expanding against pressure. The 

 amount of work here performed was accurately known, 

 the amount of heat consumed was also accurately known, 

 and from these data Mayer determined the mechanical 

 equivalent of heat. Even in this first paper he is able to 

 direct attention to the enormous discrepancy between the 

 theoretic power of the fuel consumed in steam-engines 

 and their useful eftect. 



Though this first paper contains but the germ of his 

 further labours, I think it may be safely assumed that, as 

 regards the mechanical theory of heat, this obscure Heil- 

 bronn physician in the year 1842 was in advance of all 

 the scientific men of the time. 



Having, by the publication of this paper, secured him- 



