CAUSES AND CONDITIONS. 407 



In ordinary language it is very convenient to speak of 

 static, as well as dynamic conditions, as causes ; I prefer, 

 however, in this treatise to divide the inseparable antece- 

 dents and concomitants of an event into static and 

 dynamic, and to use the term ' cause ' in a much more 

 restricted sense, viz., as meaning that exertion of physical, 

 chemical, or other natural force, which produces a change 

 or effect ; and to employ the term ' static conditions ' to 

 indicate the other inseparable circumstances of an event. 

 In this sense active forces are the only real causes, and 

 other inseparable circumstances are static conditions ; this 

 makes the meaning of the terms much more definite, and 

 enables this part of the subject to be classified and treated 

 in a more satisfactory manner. Causes are, in this aspect, 

 dynamical phenomena only. Forces may, however, be 

 said in a special sense to ' act ' without producing change 

 or motion of the mass or molecules ; as for instance, when 

 gravity acts to retain bodies on this earth ; magnetism 

 acts to support an armature ; or cohesion acts to keep the 

 particles of a body together ; but in this kind of action 

 there is no consumption of power or conversion of energy, 

 and the phenomena are purely statical. The great source 

 of terrestrial dynamic causation is the energy received from 

 the sun, and the sun is the great primary cause of the 

 various changes or dynamic effects occurring upon this 

 globe. As early as the year 1833, Sir J. Herschel stated 

 that ' the sun's rays are the ultimate source of almost every 

 motion which takes place on the surface of the earth.' 



All physical and chemical phenomena, also, whether 

 causes or effects, may be divided into statical and dyna- 

 mical, and the latter may be conveniently regarded as 

 being composed of the former, plus motion. Static phe- 

 nomena may also be regarded as being more abstruse than 

 dynamic ones, because change is a chief condition of 



