Voi,. 7, 1921 
BIOLOGY: A. J. LOTKA 
193 
From Helm's 2 standpoint, money would represent the most fluid form 
of economic energy, convertible freely into any other form of economic 
energy. Attention to this r61e of money is also drawn by Ostwald, who, 
however, expressly makes the reservation that money, although bearing 
a certain resemblance to energy, is not essentially identical therewith. 3 
Nevertheless, as we all know, money is convertible, by purchase upon 
the market, into various forms of energy, at rates somewhat variable, 
yet in some manner determinate. 
The question therefore arises, what is it that determines the ratio of 
conversion of various forms of energy by exchange upon the market? 
The physicist is familiar with two kinds of conversion factors of energy. 
The first kind of factor is that which enters into the analytical expres- 
sion of the first law of thermodynamics, the expression of the constancy 
in ratio of the amounts of several forms of energy replacing each other in 
physical transformations. 
The second kind of factor relates to that fraction of energy transformed, 
which can be recovered in a selected form, and expresses the "efficiency" 
of the transformation or of the transformer taken in view. 
It is one of the central data of thermodynamics that the equivalence 
factor is always independent of the mechanism by which the transfor- 
mation is effected, while the efficiency factor is thus independent in the 
ideal case of a reversible transformation 
It is this independence which makes the two laws of thermodynamics 
so fertile as tools for drawing conclusions regarding the course of physical 
events. Anyone who has ever sought to show a perpetual motion inventor 
just why his machine cannot work will appreciate the economy of thought 
and language which is secured by direct application of these principles. 
Now in the transformation of energy by economic exchange upon the 
market we are dealing with a third type of conversion factor. The physical 
relations here involved are so complex that we are apt to overlook al- 
together that they are physical. Still less do we ordinarily recognize 
their precise character. 
A simple example may help to clarify the view: the case of the auto- 
matic vending machine, the penny-in-the-slot chocolate dispenser, for 
instance. 
The salient facts here are : 
1. A definite amount of money brings in exchange a definite amount of 
commodity (and of energy). 
2. The physical process is a typical case of "trigger action," in which 
the ratio of energy set free to energy applied is subject to no restricting 
general law whatever (e.g., a touch of the finger may set off tons of dyna- 
mite). 
3. In contrast with the case of thermodynamic conversion factors, the 
