DIFFICULTIES XOT ALWAYS EXPLAINED. ]5fi 



as a rule, acts beneficially in all cases ; salts of ammonia 

 are especially valuable for cereals, siiperpliosphate of lime 

 for turnips ; bone earth and ashes will perceptibly in- 

 crease the produce of fruitful clover-fields, and, in like 

 manner, a supply of lime will often make a field fruitful 

 for clover, though otherwise unable to bear it. 



But upon fields which have become, as it is termed, peas 

 or clover sick, that is, have lost their power of producing 

 these plants, all these matters otherwise favourable for 

 their growth exercise beyond a certain time no further 

 beneficial action. It is this fact in particular which 

 embarrasses the practical farmer, and makes him doubt 

 the lessons taught by science. 



When the farmer is compelled to give up for many 

 years the cidtivation of plants which he had found remu- 

 nerative, and science has no power to help him over his 

 difficulties, what is the use of theory ? So says the agri- 

 cultmist who is himself unacquainted with the essence of 

 theory. 



It is a common error to fancy that an accurate Imow- 

 ledge of theory will give the power of explaining all 

 cases that occur. Theory of itself does not explain a 

 single phenomenon in astronomy, mechanics, physics, or 

 chemistry ; it studies and points out the causes which lie 

 at the foundation of all phenomena, not the special causes 

 upon which an individual phenomenon depends. 



Theory requires that the causes which govern each 

 individual case should be sought out one by one, and then 

 the explanation is the proof or exposition of the manner 

 in which they work together to produce the particular 

 fact. It teaches us what to look for, and how to employ 

 proper experiments in the discovery. 



The reason why we have arrived at no conclusions 

 about the facts just mentioned, depends chielly upon this, 



