SOLAR LIGHT AND HEAT: 



THE SOURCE, AND THE SUPPLY. 



CHAPTER I. 



INTRODUCTION. 



/^RAVITATION is commonly defined to be 

 " the force of attraction, by which all por- 

 tions of matter tend towards each other," leaving 

 the mechanical cause of this force unexplained. 



It was not without reason that D'Alembert 

 affirmed, " Philosophers are bewildered by the 

 spectacle of a falling stone." The bewilderment 

 of the illustrious Newton is manifest on referring 

 to the earliest edition of his " Principia," in which 

 he says, " The ultimate particles of matter are 

 endued with inherent forces, or powers of attrac- 

 tion and repulsion." Subsequently, in treating of 

 the universal attraction of gravitation, he says : 

 " Gravity must be caused by an agent acting con- 

 stantly, and according to certain laws ; but whether 

 this agent be material or immaterial, I leave to 

 the imagination of my readers." 



In describing the properties of matter, he after- 

 ward affirms, as the result of the long-continued 



