PREFACE. 



THE work here offered to the public will be found 

 suited, it is hoped, to two classes of readers. There 

 is a numerous class of intelligent persons who do not 

 find it convenient to possess themselves of all the more 

 important conclusions of the physical sciences by a re- 

 sort either to original memoirs or to formal scientific 

 treatises, but who nevertheless recognize the great inter- 

 est of the developments of recent science, and would be 

 glad to be put in a position to take a panoramic survey 

 of its grand generalizations. Such an opportunity the 

 author has aimed to present. 



The work will also be found useful as an aid in re- 

 view. The student may plod ever so diligently and ever 

 so intelligently through the details of a science; he is 

 apt to gain only vague impressions and floating ideas, 

 unless enabled to take a comprehensive survey of the 

 field, with the details all left in the background, and the 

 great outlines and prominent landmarks all brought sa- 

 liently into proper relations to each other. As the en- 

 gineer, who may have completed the most elaborate sur- 

 vey of a region, requires at last to contemplate it from 

 some elevated hill-top to gain a vivid conception of the 

 landscape as a whole, so the student needs to be lifted 

 up to a position where he may enjoy a bird's-eye view 



