ELEMENTAKY MAGNETISM. 345 



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 vege- 

 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- 



