234 



ATMOSPHERE. 



with a pair of very small ear-shaped tentacula above ; 

 the vent is iu the middle of the right side of the pos- 

 terior mass. The organs of respiration are unknown. 

 De Blainville places this genus in the family Akera, 

 of the order Monopleurobranchiata, class Parace- 

 2>halophora. The only species described is Peron's 

 Atlas. 



ATMOSPHERE. The mass of invisible, trans- 

 parent, and dry fluid, which surrounds the whole 

 globe, and forms not only the grand natural medium 

 of communication between the land and the waters, 

 but the medium by which the remotest points on the 

 whole surface are enabled to communicate with and 

 be of use to each other. 



It has been already stated in the article AIR, 

 which see, that the mechanical and chemical proper- 

 ties of this fluid form no part of natural history ; and 

 some of its local uses to plants and animals have 

 been pointed out in that article. The fact is, that 

 the atmosphere is so very important, and the uses 

 of it, both in nature and in art, are so many, that 

 the entire knowledge of it forms many sciences, and 

 some of the applications of those sciences are of vast 

 importance in the arts of life. We may remark, in 

 passing, that it is to the atmosphere that man owes 

 his first and grand triumph over all the other animals. 

 He kindles a fire, and all the savage tyrants of the 

 world avoid its radiance, as if it were the contriv- 

 ance of powers superior to theirs. This fire once ob- 

 tained, the uses of it are innumerable, and yet the 

 half of them may not have hitherto been discovered. 

 Without it, we could dress no food, we could have 

 no metals, no glass, no porcelain, no bricks for build- 

 ing, no steam, no gunpowder, nothing, in short, worth 

 the living for ; and we could have no fire without the 

 atmosphere. Yet this is but one of its numerous 

 uses, and what we are sometimes disposed to con- 

 sider a trifling one ; at least it is of so very common 

 and familiar a nature that we are apt to pass it over 

 unheeded. Our acquaintance with the weather, too, 

 on which our comfort, our health, and well-being 

 rests, so far as we are cultivators or dependent 

 upon cultivation, (and who is not either the one, 

 the other, or both ?) are so much involved, is 

 wholly a matter of the knowledge of the atmo- 

 sphere. The uses of the atmospheric fluid as a 

 power, whether in the turning of mills and other 

 machinery, the wafting of ships across the seas and 

 oceans or quite round the globe, or any other pur- 

 pose, to which as a power it can be applied, are well 

 worthy o,f our study and our admiration. In these 

 respects, it is both a wonderful and a wayward thing; 

 and judging of it according to our plans and wishes, 

 we may say in the language of Holy Writ, " the 

 wind bloweth where it listeth." But when we take 

 all nature into consideration it is not so ; for the 

 blowing of the wind is an effect, a natural effect, and 

 is as dependent upon its cause and as proportional to 

 it as any of those effects, over which and their causes, 

 we suppose that we have the most perfect control. 



The blowing of the wind, though not in itself sim- 

 ply, or in the notions that we have of it as a mecha- 

 nical power, one of the natural history properties of 

 the atmosphere, is yet one which tends very natu- 

 rally to produce these, because it is the mobility of 

 the atmosphere, or the ease with which it is put in 

 motion, which is the foundation of many of the most 

 important functions which it performs in the eco- 

 nomy of nature. 



In the economy of the earth's surface, and as far 

 below that surface, whether it bn land or water, as 

 life and growth are concerned, the atmosphere may 

 be considered pre-eminently above every other agent, 

 as the messenger by whose kindly offices the system 

 of nature is preserved, and but for which every living 

 thing must, as a necessary result of those common 

 laws of matter which are still as necessary to the per- 

 fection of the whole, as the agency of the atmo- 

 sphere is, speedily and inevitably perish. Whether, 

 it there were no atmosphere, water could exist upon 

 the surface of our earth, is a question which we are 

 not, in a merely natural history view of the matter, 

 called upon to decide ; but analogy points rather to 

 the negative ; and some persons believe that we 

 have, in the body which is situated the nearest to our 

 earth, the moon, an example of an atmosphereless 

 and waterless globe. W T e cannot examine the sur- 

 face of the moon, close at hand, and with our naked 

 eyes, as we can do that of the earth along which our 

 path lies ; but science, by furnishing us with the 

 telescope, gives us some advantages in examining the 

 moon, which we cannot have in examining the earth. 

 The portion of the earth's surface which our vision 

 can in ordinary cases command, is a mere speck as 

 compared with the whole ; and when we ascend to 

 the utmost elevation to which a balloon has floated, or 

 the foot of man trod the mountain, and take with us 

 there the very best instruments which human inge- 

 nuity has constructed, our horizon is still very limited, 

 and though (of which we can have no security) the 

 clouds favour our observation, all that we can by possi- 

 bility see, gives us no adequate idea of what the globe 

 which we inhabit is like, in all its lands and seas, and all 

 its zones and climates, with their varied productions. 



But when we examine the moon through an instru- 

 ment of sufficient power, we can judge of it as a whole, 

 that is we can command, wholly or nearly, an entire 

 hemisphere, or half of its surface. It is true that we 

 do not see the entire hemisphere in the same position : 

 we see the centre of it in plane, and the rest more and 

 more obliquely, till the parts at the circumference are 

 seen in profile. But this is a very great advantage ; 

 because we have planes, elevations, and also views in 

 all degrees of obliquity, the information which we get 

 from each of which, corrects and perfects that which 

 we get from the others. Not only this ; but in the 

 course of the waxing and Waning of the moon, from the 

 first streak of illuminated surface that appears a little 

 after sunset in the west,, to the last vanishing one 

 which appears a little before sunrise in the east, we 

 have the light falling upon the same portions of the 

 surface at a great variety of angles, and thus revealing 

 them by all the advantages of light and shade, which 

 are most essential elements in the judgments which 

 we form of objects on the earth from sight. 



The 240,000 miles which the moon is, on the 

 average, distant from the earth, is, no doubt, a long 

 distance, although not more in absolute length than 

 that passed over by a sailor, who makes ten or twelve 

 voyages to India. But to the eye it is really nothing, 

 for the eye can see a star so far off, that iJOO,000,000 

 of miles is not a measurable fraction of the distance. 

 The distance of common vision, and the distance of 

 the moon, is therefore a question of the relative mag- 

 nitude of surfaces equally visible ; and it is not over- 

 straining the fact to say that, with the very best 

 instruments, a portion of the moon's surface ten miles 

 square, nay, one mile square, may be seen as minutely 



