10 INTRODUCTION. 



Why of Heat 4. As the most of them depend on changes 



and light? _ . . 



of temperature, it is necessary in the first 

 part of the work to consider the laws and effects of 

 Heat. As these laws are best understood from their 

 analogy to the laws of Light, and as Light has an import- 

 ant influence in many chemical processes, a brief chapter 

 on Light precedes the chapter on Heat and its various 

 effects. 



5. As many, and perhaps all chemical 



Why is Elec- . . t , 



tricity intro- changes, are accompanied by electrical 

 duced? phenomena, it is also important to dwell 



briefly on the subject of Electricity before proceeding 

 to what is more strictly the science of Chemistry. 

 The first part of this work is, therefore, devoted to the 

 consideration of these subjects ; or, in other words, to 

 the Science of Physics. 



