ELEMENTARY MAGNETISM. 397 



electricity with those of sound with the pressures and 

 motions of liquids and gases, whether at rest or 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 attention of him who 

 would cultivate it profoundly. Astronomy is the ap- 

 plication 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 atoms and molecules to unite or to fall 

 asunder. Electricity exerts a similar power. Through 

 their ability to separate nutritive compounds into their 

 constituents, the solar beams build up the whole veger 

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

 the self-same beams causes hydrogen and chlorine to 

 unite with sudden explosion, and to form by their com- 

 bination a powerful acid. Thus physics and chemistry 

 intermingle. Physical agents are, however, employed 

 by the chemist as a means to an end ; while in physics 

 proper the laws and phenomena of the agents them- 

 selves, both qualitative and quantitative, are the pri- 

 mary 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. From the domain of 

 physics, which would be unmanageable as a whole, I 

 select as a sample the subject of magnetism. I might 

 readily entertain you on the present occasion with an 

 account of what natural philosophy has accomplished. 

 I might point to those applications of science of which 

 we hear so much in the newspapers, and which are 

 so often mistaken for science itself. I might, of course, 

 ring changes on the steam-engine and the telegraph, 

 the electrotype and the photograph, the medical appli- 



