General Objects and Principles. 3 



thus thrown back to your eyes, and which causes 

 you to see a figure as distinctly as if you looked 

 upon the figure itself. This shall also be ex- 

 plained to you ; as well as the reason why when 

 you look upon the ground, at a wainscot, or on 

 a rough unpolished table, you see nothing of the 

 kind. 



When you look through some glasses you see 

 things much bigger than they really are, or mag- 

 nified; that is, made larger. When you look 

 through others you see them less than they appear 

 to your eyes, or diminished. What is there, 

 then, in the one glass that it should cause things 

 to appear larger than they do to your natural 

 sight: or, in the other, that they should seem 

 so diminished ? Yet this too will be explained ; 

 and you may, by certain rules, be taught to 

 calculate how much larger or smaller any glass 

 will make an object appear, before you look 

 through it. 



You cannot be unacquainted with that tre- 

 mendous noise, which the ignorance of the an- 

 tients considered as an indication that their god 

 Jupiter was in a passion. We call it thunder. 

 But what is thunder ? You have also probably 

 seen fire descend in streams from the clouds, or 

 pass instantaneously from one cloud to another ; 

 and after darting first to one side, and then to 

 the other, several times, come to the earth with 

 a zig-zag kind of motion. This is lightning, 

 and it proves fatal wherever it strikes: it kills 



