ELEMENTARY MAGNETISM. 345 



ence of mechanics is a portion of natural philosophy, 

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

 tention of him who would cultivate it profoundly. As- 

 tronomy 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 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 vegetable world, and by it the ani- 

 mal world. The touch of the self-same beams causes 

 hydrogen and chlorine to unite with sudden explosion, 

 and to form by their combination 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 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. 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 

 BO 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- 

 cations of physics, and the various other inlets by 

 which scientific thought filters into practical life. That 

 v/ould be easy compared with the task of informing 



