INTRODUCTION. 3 



forces of nature. The wind was the breath of one 

 god, and the lightning a bolt thrown from the 

 hands of another. 



With advancing thought the ideas of polythe- 

 ism later gave place to the nobler conception of 

 monotheism. But for a long time yet the same 

 ideas of the supernatural, as related to the natu 7 

 ral, retained their place in man's philosophy. 

 Those phenomena which he thought he could 

 understand were looked upon as natural, while 

 those which he could not understand were looked 

 upon as supernatural, and as produced by the di- 

 rect personal activity of some divine agency. As 

 the centuries passed, and man's power of observa- 

 tion became keener and his thinking more logical, 

 many of the hitherto mysterious phenomena be- 

 came intelligible and subject to simple explana- 

 tions. As fast as this occurred these phenomena 

 were unconsciously taken from the realm of the 

 supernatural and placed among natural phenom- 

 ena which could be explained by natural laws. 

 Among the first mysteries to be thus compre- 

 hended by natural law were those of astronomy. 

 The complicated and yet harmonious motions of 

 the heavenly bodies had hitherto been inexplica- 

 ble. To explain them many a sublime concep- 

 tion of almighty power had arisen, and the study 

 of the heavenly bodies ever gave rise to the 

 highest thoughts of Deity. But Newton's law of 

 gravitation reduced the whole to the greatest 

 simplicity. Through the law and force of gravi- 

 tation these mysteries were brought within the 

 g;asp of human understanding. They ceased to 

 be looked upon longer as supernatural, and be- 

 came natural phenomena so soon as the force of 

 gravitation was accepted as a part of nature. 



