174 ON THE ECONOMICAL PRODUCTION OF 



termed thermo-dynamic engines, include steam engines, air 

 engines, &c. 



The process whereby muscular effort is developed in the 

 living machine is, as might be expected, involved in great 

 obscurity. Professor Magnus has endeavoured to prove that 

 the oxygen inspired by an animal does not immediately enter 

 into combination with the blood, but is mechanically conveyed 

 by it to the capillary vessels within the muscles^ where it 

 combines with certain substances, converting them into 

 carbonic acid and water. The carbonic acid, instead of 

 oxygen, is then absorbed by the blood, and is discharged 

 therefrom when it reaches the lungs. Taking this view, we 

 may admit with Liebig, that at each effort of an animal a por- 

 tion of muscular fibre unites with oxygen, and that the whole 

 force of combination is converted by some mysterious process 

 into muscular power, without any waste in the form of heat. 

 This conclusion, which is confirmed by the experiments 

 related in a joint memoir by Dr. Scoresby and myself, 

 shows that the animal frame, though destined to fulfil so 

 many other ends, is as an engine more perfect in the economy 

 of vis viva than any human contrivance. 



The electro-magnetic engine presents some features of 

 similarity to the living machine, and approaches it in the 

 large proportion of the chemical action which it is able to 

 evolve as mechanical force. If we denote the intensity of 

 current electricity when the engine is at rest by a, and the 

 intensity of current when the engine is at work by b, the 

 proportion of chemical force converted into motive force 



will be - — , and the quantity wasted in the form of heat 



will be — . Now from my own experiments, I find that 

 a 



each grain of zinc consumed in a Daniell's battery will raise 



the temperature of a lb. of water 0°-1886; and that the heat 



which can increase the temperature of a pound of water by 



