160 BOOK OP NATURE LAID OPEN. 



Another wonderful property of the air is its invi- 

 sibility; for, although it can be heard in the howling 

 of the tempest, and felt in the pressure of the gale, 

 and notwithstanding the number of bodies that con- 

 tinually mix with its substance, it is still too fine to 

 be seen by the sharpest eye. 



Every object around us is visible, except the air; 

 and happy it is for us that it is so ; for, had it been 

 otherwise, farewell to all the delightful prospects that 

 charm the eye; farewell to all the bright beauties of 

 creation. Nature must have put on a sombre aspect, 

 and, instead of those delightful regions of light and 

 cheerfulness in which we are placed, our habitations 

 would have been surrounded by the doleful shades 

 of a dusky covering, and environed with a mantle 

 of darkness and despair. 



But, although the atmosphere is of itself invisible 

 to the sight, it is the happy medium of light and heat. 

 The air is found to moderate the rays of light, to dis- 

 sipate their violence, and to spread an uniform lus- 

 tre over every object. Were the beams of the sun 

 to dart directly upon us, without passing through this 

 protecting medium, they would either burn us up at 

 once, or blind us with their effulgence; but, by go- 

 ing through the air, they are reflected, refracted, and 

 turned from their course a thousand different ways, 

 and thus are more evenly diffused over the face of 

 nature. But this is not all ; for, by means of the air, 

 the beams of the sun are not only rendered tolerable, 

 and the rays of light more copiously diffused through- 

 out creation, but the advantages of heat and light are 



