INTERMIXTURE OF EFFECTS. 497 



cause. But the body does not only move in that manner 

 unless counteracted ; it tends to move in that manner even 

 when counteracted ; it still exerts, in the original direction, 

 the same energy of movement as if its first impulse had been 

 undisturbed, and produces, by that energy, an exactly equiva- 

 lent quantity of effect. This is true even when the force 

 leaves the body as it found it, in a state of absolute rest ; as 

 when we attempt to raise a body of three tons weight with 

 a force equal to one ton. For if, while we are applying this 

 force, wind or water or any other agent supplies an additional 

 force just exceeding two tons, the body will be raised; thus 

 proving that the force we applied exerted its full effect, by 

 neutralizing an equivalent portion of the weight which it 

 was insufficient altogether to overcome. And if while we are 

 exerting this force of one ton upon the object in a direction 

 contrary to that of gravity, it be put into a scale and weighed, 

 it will be found to have lost a ton of its weight, or in other 

 words, to press downwards with a force only equal to the 

 difference of the two forces. 



These facts are correctly indicated by the expression 

 tendency. All laws of causation, in consequence of their 

 liability to be counteracted, require to be stated in words 

 affirmative of tendencies only, and not of actual results. In 

 those sciences of causation which have an accurate nomen- 

 clature, there are special words which signify a tendency to 

 the particular effect with which the science is conversant; 

 thus pressure, in mechanics, is synonymous with tendency to 

 motion, and forces are not reasoned on as causing actual 

 motion, but as exerting pressure. A similar improvement 

 in terminology would be very salutary in many other branches 

 of science. 



The habit of neglecting this necessary element in the 

 precise expression of the laws of nature, has given birth to 

 the popular prejudice that all general truths have exceptions , 

 and much unmerited distrust has thence accrued to the con- 

 clusions of science, when they have been submitted to the 

 judgment of minds insufficiently disciplined and cultivated. 

 The rough generalizations suggested by common observation 

 VOL. i. 3 



