LESSONS /A 7 PHYSICS. 11 



vulsive movements of a frog's legs when in contact with iron and 

 copper, started in the mind of Galvani a train of thought which 

 grew and developed into the telegraph, telephone, ocean cables, 

 electric motors, electric light, etc. From other ideas, suggested 

 by the bobbing lid of a kettle partly filled with boiling water, 

 have resulted the steam engine and our modern steamship and 

 railway systems, which have revolutionized every form of in- 

 dustry. 



But the chief value of science is not in its practical applica- 

 tions, valuable as they may be, but rather in the development of 

 the scientific method of thought and investigation. That train- 

 ing of the mind, which grows out of the nature of scientific work, 

 is of the highest educational value. The collection of facts, the 

 study of their varied relations, the testing of conclusions by 

 comparison and experiment, result in habits of thought that are 

 valuable in any field of human endeavor. Such work tends to 

 make man a self-reliant, independent thinker. The field of science 

 is the universe of matter. As more and more of this field was 

 opened by investigators, it was gradually divided into depart- 

 ments and sub-departments until there are as many as fifty 

 separate lines of scientific inquiry, either one of which would 

 furnish material enough to employ the life-time of an industrious 

 student. 



The boundaries of these departments are, in many cases, not 

 sharply defined. The different parts of the universe are so inti- 

 mately related that any scheme of classification must be largely 

 artificial. 



Of these departments, physics and chemistry seem to be funda- 

 mental. Physics deals with those phenomena of matter that do 

 not involve a change of substance, but simply change of position, 

 form or condition. Chemistry deals with those phenomena which 

 do involve a change of substance, as the various kinds of com- 

 bustion and decay. But the distinction between these branches 

 of science is not very exact. In fact there is a wide field of com- 

 mon ground between them. 



Every body, whether mineral, vegetable or animal, whatever 



