DISCOVERY OF STATIC CONDITIONS. 435 



such a case the desired result is obtained by the method 

 of means or averages ; this method equalises all irregular 

 or accidental changes, and thus enables the regular ones 

 to be perceived. It is very largely employed in meteoro- 

 logical investigations, to determine the average height of 

 the mercury in a barometer, the average temperature of 

 the earth, or velocity of the wind, the changes of magnet- 

 ism, &c., at any period ; also to find the true sea-level or 

 height of tide, and so on. In this way, quantitative de- 

 terminations often enable us to discover a cause, or an 

 effect, and its amount at the same time. 1 



CHAPTEE XLVIL 



DISCOVERT OF STATIC CONDITIONS. 



STATIC conditions are essentially of greater importance 

 than dynamic ones, and the minute circumstance which 

 excites, liberates, determines, transmutes, directs, and 

 guides a force, is often more influential (especially when 

 aided by time) than the force itself. This great truth is 

 manifested in every science and branch of knowledge. In 

 the science of heat, unless the fire of a locomotive be 

 excited by applying a match, no steam will be generated ; 

 in that of mechanical power, unless the valve of the engine 

 is open, to liberate steam from the boiler into the cylinders, 

 no motion occurs ; and upon a railway, unless the points 

 of the rails are properly placed, an accident soon occurs ; 

 in that of electricity, unless a telegraphic circuit through- 

 out is complete, no message can be sent. In the sciences of 

 physiology and psychology also the same truth appears ; 



1 See also page 423, 



F F 2 



