364 FRAGMENTS OF SCIENCE 



nomena and laws of magnetism and 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 nat- 

 ural philosophy, though at present so large as to need the 

 exclusive attention of him who would cultivate it pro- 

 foundly. 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 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 animal world. The 

 touch of the self-samfc beams causes hydrogen and chlo- 

 rine to unite with sudden explosion, and to form by their 

 combination a powerful acid. Thus physics and chem- 

 istry 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 se- 

 lect as a sample the subject of magnetism. I might read- 

 ily 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 mis- 



