THE EARTH. 121 



to venture once more into the gulf for further discoveries, he at first 

 refused ; but the king, desirous of having the most exact information 

 possible of all things to be found in the gulf, repeated his solicita- 

 tions; and, to give them still greater weight, produced a larger cup 

 than the former, and added also a purse of gold. Upon thfise con- 

 siderations, the unfortunate Pessacola once again plunged into the 

 whirlpool, and was never heard of more." 



CHAPTER XVIII. 



A SUMMARY ACCOUNT OF THE MECHANICAL PROPERTIES OP AIR. 



HAVING described the earth and the sea, we now ascend into that 

 fluid which surrounds them both; and which, in some measure, sup- 

 ports and supplies all animated nature. As upon viewing the bottom 

 of the ocean from its surface, we see an infinity of animals moving 

 therein, and seeking food ; so, were some superior being to regard 

 the earth at a proper distance, he might consider us in the same 

 light: he might, from his superior station, behold a number of busy 

 little beings, immersed in the aerial fluid, that every where surrounds 

 them, and sedulously employed in procuring the means of subsist- 

 ence. This fluid, though too fine for the gross perception of its in- 

 habitants, might, to his nicer organs of sight, be very visible; and, 

 while he at once saw into its operations, he might smile at the varie- 

 ties of human conjecture concerning it : he might readily discern, 

 perhaps, the height above the surface of the earth to which this fluid 

 atmosphere reaches ; he might exactly determine that peculiar form 

 of its parts which gives it the spring or elasticity with which it is en- 

 dued ; he might distinguish which of its parts were pure, incorrup- 

 tible air, and which only made for a little time to assume the appear- 

 ance, so as to be quickly returned back to the element from whence 

 it came. But as for us, who are immersed at the bottom of this 

 gulf, we must be contented with a more confined knowledge ; and, 

 wanting a proper point of prospect, remain satisfied with a combina- 

 tion of the effects. 



One of the first things that our senses inform us of is, that although 

 the air is too fine for our sight, it is very obvious to our touch. Al- 

 though we cannot see the wind contained in a bladder, we can very 

 readily feel its resistance; and though the hurricane may want colour, 

 we often fatally experience that it does not want force. We have 

 equal experience of the air's spring or elasticity : the bladder, when 

 pressed, returns again upon the pressure being taken away ; a bottle, 

 vhen filled, often bursts, from the spring of air which is included. 



So far the slightest experience reaches ; but, by carrying experi- 

 ment a little farther, we learn, that air also is heavy ; a round glass 

 vessel being emptied of its air, and accurately weighed, has been 

 found lighter than when it was weighed with the air in it. Upon 

 computing the superior weight of the full vessel, a cubic foot of air it 

 found to weigh something more than an ounce. 



