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essentially depends. Again, had the density of 

 the air heen much greater or less than it is, the 

 energies of man would have been, on the one 

 hand, oppressed by it, as by an unnatural load, 

 and on the other, insufficiently sustained by it, 

 as by a defective support. We all feel more or 

 less of these effects on every sudden change in 

 the barometrical pressure, and, still more remark- 

 ably, on either descending below the water in a 

 diving-bell, when the air becomes preternatural- 

 ly dense, or ascending into the atmosphere in 

 an air-balloon, when it becomes preternaturally 

 rare ; and had either of these states been per- 

 manent, its effects on the human economy must 

 have been most prejudicial. Among other things, 

 the senses of both smell and hearing, both which 

 depend for their perfection on a medium density 

 of the air, would have been either insupportably 

 intense or defective. Further, with regard to 

 light the first of created things, and the crea- 

 tion of which is described in the most sublime 

 passages of written language this is precisely 

 such as is adapted, when reflected from the ob- 

 jects which surround us, to afford the proper 

 stimulus to the organ of vision ; and, even the 

 colours of the most common objects are those 

 which are most refreshing to the sense of sight. 

 The blue sky which surrounds us, could we, 

 with advantage, change in colour ? This colour, 

 which is owing to the thin watery vapours float- 

 ing in the atmosphere, and reflecting peculiar 

 rays of lights the blue and the violet, might 



