LESSON IV. 



ON MERCURY. 



First Mercury amidst full tides of light, 



Rolls next the Sun, through his small circle bright; 



All that dwell there must be refin'd and pure ; 



Bodies like ours, such ardour can't endure; 



Onr earth would blaze beneath so fierce a ray, 



And all its marble mountains waste away. BAKER. 



JlOWEVER ignorant we are of the nature of 

 qualities, and how much soever their mode of ope- 

 ration is concealed from us, if it be but admitted 

 that they act in right lines, and that they are pro- 

 pagated from a point, or body, as from a center, 

 then it may be demonstrated in a strictly geome- 

 trical manner, that their energy, or intensity, di- 

 minishes in a duplicate proportion of the distance 

 from that center. Thus, for instance, suppose a 

 person whom I will call Thomas, stands at ten feet 

 distance from a fire, and another, whom I will call 

 James, stands twenty feet from the fire ; if they 

 are similarly situated in all respects but that of 

 distance, it may be demonstrated, that the fire will 

 impart four times as much heat to Thomas as to 

 James ; that is, Thomas's heat is to James's, as 

 the square of James's distance from the fire is to 

 the square of Thomas's distance from it. 



Considering the sun as the center from whence 

 proceed those rays, or particles, which meeting 



with 



