ACTIVE AND POTENTIAL CAUSES. 413 



Real causes may be either active or potential, i.e. 

 stored up in a latent state ; for instance, a spring may be 

 wound up, and the power expended in winding may 

 remain potential in it during almost any length of time 

 until the spring is released. A concussion imparted to 

 dynamite is the apparent cause of the explosion, but the 

 real cause is the potential force existing in the materials ; 

 the shock only liberates a small amount of the power, and 

 the vibration or heat caused by that liberated power sets 

 free the remainder. In this case the shock only deter- 

 mines or excites the entire result, and ' great effects from 

 little causes spring.' In a similar manner the heat of 

 an ordinary fire is not caused by the flame of the match 

 applied to light the fire, but to the liberation of the 

 stored-up energy of the burning materials ; the flame of 

 the match excites only a commencement of the action 

 by supplying the requisite temperature. All combustible 

 bodies and most of the elementary substances, especially 

 the highly positive and negative ones, such as potassium, 

 sodium, magnesium, hydrogen, &c., and oxygen, fluorine, 

 chlorine, sulphur, phosphorus, &c., contain great potential 

 chemical energy or stored-up chemical power; strong 

 acids and alkalies also possess it. A real cause, according 

 to the doctrine of conservation of energy, is always equiva- 

 lent in power to its total effect or effects ; but an exciting 

 one varies in amount, and is often disproportionately 

 small, and may be termed 4 homoeopathic ;' for instance, 

 a very minute spark will determine the explosion of an 

 unlimited quantity of gunpowder, the slightest touch of a 

 wire will complete an electric circuit and send a signal 

 round the earth, &c. Every potential power may be con- 

 sidered a self-determining one, when it is liberated. 



Different causes possess very different degrees of gene- 

 rality, some are extremely general ; for instance, mecha- 



