A LECTURE ON MAGNETISM. 359 



gases, whether in a state of translation or of undulation. 

 The science of mechanics is a portion of natural philosophy, 

 though at present so large as to need the exclusive atten- 

 tion of him who would cultivate it profoundly. Astronomy 

 is the application of physics to the motions of the heavenly 

 bodies, the vastness of the field causing it, however, to be 

 regarded as a department in itself. In chemistry physical 

 agents play important parts. By heat and light we cause 

 bodies to combine, and by heat and light we decompose 

 them. Electricity tears asunder the locked atoms of com- 

 pounds, through their power of separating carbonic acid into 

 its constituents ; the solar beams build up the whole vege- 

 table world, and .by it the animal, while the touch of the 

 self-same beams causes hydrogen and chlorine to unite with 

 sudden explosion and form by their combination a powerful 

 acid. Thus physics and chemistry intermingle, physical 

 agents being employed by the chemist as a means to an 

 end ; while in physics proper the laws and phenomena of 

 the agents themselves, both qualitative and quantitative, 

 are the primary objects of attention. 



My duty here to-night is to spend an hour in telling how 

 this subject is to be studied, and how a knowledge of it is 

 to be imparted to others. When first invited to do this, I 

 hesitated before accepting the responsibility. It would be 

 easy to entertain you with an account of what natural phi- 

 losophy has accomplished. I might point to those applica- 

 tions of science regarding which we hear so much in the 

 newspapers, and which we often find mistaken for science 

 itself. I might, of course, ring changes on the steam- 

 engine and the telegraph, the electrotype and the photo- 

 graph, the medical applications of physics, and the million 

 other inlets by which scientific thought filters into prac- 

 tical life. That would be easy compared with the task 

 of informing you how you are to make the study of physics 

 the instrument of your own culture, how you are to pos- 



