THEODOKE II. BUI. LOCK 3 



If we recognize the existence of such a class of phenomena in nature, there 

 arises the question how to cUstinguish triggers from non-triggers. The main 

 contrast, it is clear, is with devices like the accelerator of a car or the key on 

 a piano, in which the application of energy does not lead to a critical point, 

 nor the independence of amplitude and time course of the output from those 

 of the input. The relation between input (pulling the trigger) and output 

 (change in position of the hammer) is a step function in the class of triggers 

 whereas it is graded over some range in non-triggered events (fig. i). 



Put in this way, it will be apparent that there can be intermediate cases. A 

 compound lever system with only a fairly critical zone, an amplifier with some 

 regeneration, indeed any nonlinear system will display somewhat intermediate 

 properties. However, in devices made or selected for a use, in general one or the 

 other alternative will be chosen — either stable dependence of output on input, 

 or a triggering action. 



The detinition does not require that the output of energy or change of state 

 niitiated upon passing the critical point be abrupt in time, only that it be abrupt 

 as a function of increasing input. We have examples of good triggers in which 

 the rate of release of energy is slow — as in launching a battleship — or voting its 

 construction ! 



There is always an energy hump, but once this is surmounted the built-in 

 features of the system determine the course of events, not the nature of the 

 pull. In useful triggers, there is generally a large amplification. 



TYPES OF TRIGGERS 



A second question which is automatically posed if we recognize the existence 

 of triggers, is whether all the cases embraced under the class are perfectly equiv- 

 alent, or whether there are subclasses. 



We may propose a subdivision on the basis of the mechanism of the critical 

 point, a) Some triggers depend for their critical point upon a spatial arrange- 

 ment of the parts, which defines the unstable state, as in the trigger in a gun 

 or the rock balanced on the edge of a cliff, b) Others depend for their critical 

 point upon the arrangement of parts within molecules or atoms, therefore upon 

 empirically determined properties of these molecules or atoms. Examples would 

 be systems poised close to the ignition point, the boiling point, the melting 

 point or even just above the freezing point because in a useful case it requires 

 an increment of energy to cool further or to seed a super-cooled system, c) A 

 third group of cases depends for the critical point upon neither of these condi- 

 tions fundamentally, but upon the relation between two or more simultaneous 

 rate functions. This will be exemplified by a bistable circuit, an autocatalytic 

 reaction or an explosion, since the critical point in each case depends on the rate 

 of energy release (or forward chemical reaction or plate current) and the rate 

 of rise of temperature of neighboring particles (or catalytic effect of products 



