188 LECTURES. 



2. Chemistry, wliicli relates to ^;^\epecul^ar phenomena of individual 

 bodies ; to the laws of their combinations ; decompositions &c. 



3. Natural Philosophy, or Physics, the branch of science witb 

 which we are to be occupied in this course of lectures, teaches the 

 laws of the general phenomena of bodies and of the agents which pro- 

 duce the changes in inorganic matter; such as the unknown cause of 

 attraction, light, heat, electricity, &c. 



These divisions of the study of the laws of inorganic matter are con- 

 ventional rather than real. 



(5.) Science assumes as its basis that the laws of nature are constant. 



The same principle is often expressed in other terms; as, 1. The 

 uniformity of causation. 2. Like causes produce like effects. 3. In 

 similar circumstances similar consequences will ensue. 



This principle is the foundation of all scientific reasoning, and is 

 collected from all experience by an original propensity or law of the 

 human mind. — [Young.'] 



(6.) Most of the phenomena of nature are presented to us as the 

 complex results of the operation of a number of laws. 



We are said to explain or give the cause of a simple fact when we 

 refer it to the law of the phenomena to which it belongs, or to a 

 more general fact ; and a compound one when we analyse it and refer 

 its several parts to their respective laws. 



(7.) The indefinite use of the term cause, has led to much confusion 

 and error. We distinguish two kinds of causes, intelligent and phy- 

 sical. 



By an intelligent cause is meant the volition of an intelligent and 

 efficient being producing a definite result. By a physical cause, scien- 

 tifically speaking, nothing more is understood than the law to which, 

 a phenomenon can be referred. 



Thus we give the physical cause of the fall of a stone or the eleva- 

 tion of the tides when we refer these phenomena to the law of gravita- 

 tion. And the intelligent cause when we refer this law to the volition 

 of the Deity. 



In 'cases where the law has not been discovered, one fact is said to 

 be the cause of another, when the latter, in some unknown way, 

 depends on the former. Before the law of universal gravitation was 

 discovered, the moon was said to be the cause of the tides, but we 

 now say, in reference to this explanation, that the true cause was 

 then unknown. 



The intelligent cause is sometimes called the moral cause, and also 

 the efficient cause. 



It is to be regretted that the use of the term cause has not been 

 restricted to the efficiency of an intelligent being, to which it alone 

 properly belongs, and from which the idea is derived. 



(8.) In the investigation of the order of nature, two general methods 

 have been proposed ; the a priori and the inductive method. 



The a priori method consists in reasoning downwards from the 

 original cognitions, which, according to the a priori philosophy, exist 

 in the mind relative to the nature of things, to the laws and phe- 

 nomena of the material -universe. 



