230 HISTORY OF 



tiire concerning it ; lie nii^ht readily discern, perhaps, the Iieigh. 

 above the surface of the earth to which this fluid atmo- 

 sphere reaches ; he might exactly determine the peculiar form 

 of its parts which gives it the spring or elasticity with which it 

 IS endued : he might distinguish which of its parts were pure 

 -ncorruptible air and which only made for a little time to assume 

 the appearance, so as to he 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 con- 

 fined knowledge ; and, wanting a proper point of prospect, remain 

 satisfied with a combination of the efl!ects. 



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. Although 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, when filled, often 

 bursts from the spring of air which is included. 



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

 periment 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 is found to weigh something more than an 

 ounce. 



From this experiment, therefore, we learn, that the earth, and 

 all things upon its surface, are every where covered with a pon- 

 derous fluid, which rising very high over our heads must bo 

 proportionably heavy. For instance, as in the sea, a man at the 

 depth of twenty feet sustains a greater weight of water, than a 

 man at the depth of but ten feet ; so will a man at the bottom 

 of a valley have a greater weight of air over him, than a man on 

 the top of a mountain. 



From hence we may conclude, that we sustain a very great 

 weight of air ; and although, like men walking at the bottom of 

 the sea, we cannot feel the weight which presses equally round 

 us, yet the pressure is not the less real. As in morals we sel- 

 dom know the blessings that surround us, till we are deprived of 



