LECTURES. 189 



The inductive method, which is the inverse of the other, is founded 

 on the principle that all our knowledge of nature must he derived 

 from experience. It therefore commences with the study of phe- 

 nomena, and ascends from these hy what is called the inductive pro- 

 cess, to a knowledge of the laws of nature. It is by this method that 

 the great system of modern physical science has been established. It 

 was used in a limited degree by the ancients, and especially by Aris- 

 totle, hut its importance was never placed in a conspicuous light until 

 the publication of the Novum Organum of Bacon. 



(9.) In the application of the inductive method to the discovery of 

 the laws of nature, four processes are usually employed, 



1. Observation^ which consists in the accumulation of facts ; by 

 watching the operations of nature as they spontaneously present them- 

 selves to our view. 



This is a slow process, but it is almost the only one, which can be 

 employed in some branches of science. For example, in astronomy. 



2. Experiment, which is another method of observation, in which 

 we bring about, as it were, a new process of nature by placing matter 

 in some unusual condition. 



This is a much more expeditious process than that of simple obser- 

 vation, and has been aptly styled the method of cross-questioning or 

 interrogating nature. 



The terra experience is often used to denote either observation or 

 experiment, or both. 



3. The inductive process, or that by which a general law is inferred 

 from particular facts. This consists generally in making a number 

 of suppositions or guesses as to the nature of the law to be discovered, 

 and adopting the one which agrees with the facts. The law thus 

 adopted is usually further verified by making deductions from it and 

 testing these by experiment ; if the result is not what was anticipated, 

 the expression of the law is modified, perhaps many times in succes- 

 sion, until all the inferences from it are found in accordance with the 

 facts of experience. 



4. Deduction, which is the inverse of induction, consists in reason- 

 ing downwards from a law wliich has been established by induction, 

 to a system of new facts. In this process the strict logic of mathe- 

 matics is employed, the laws furnished by induction standing in the 

 place of axioms. Thus all the facts relative to the movements of the 

 heavenly bodies, have been derived by mathematical reasoning from 

 the laws of motion and universal gravitation. 



Induction and deduction are sometimes called analysis and syn- 

 thesis. 



(10.) When one system of facts is similar to another, and when 

 therefore we infer that the law of the one is similar to the law of the 

 other we are said to reason from analogy. 



This kind of reasoning is of constant use in the process of induction, 

 and is founded on our conviction of the uniformity of the laws of 

 nature. 



In the process of the discovery of a law, the supposition which we 

 make as to its nature, must be founded on a physical analogy, between 



