956 
Proceedings of the Pioyal Society 
our most important source of energy — coal ; the complex problems 
of its ratio of exchange, and the causes of its fluctuation, of the 
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Fig. 3, — The lower portion of the diagram is intended to contain the details 
of production and consumption; the upper to record the changes of matter and 
energy _in the process. 
external and internal relations of the producer-automata, of the 
