THE DAY. 



magnitude, covers a certain part of the Leavens, and different 

 points of this disc arrive at a given point of the firmament at 

 different moments ; so that when we speak of the moment the sun 

 passes any given point of the heavens, our words have no definite 

 meaning unless we specify what point of the sun's disc our obser- 

 vation is applied to. The point in question is of course the centre 

 of the disc, the successive returns of which to a certain position 

 in the heavens must be observed. 



The point most convenient in all respects for such an observa- 

 tion is the highest to which the sun rises in its diurnal course 

 across the heavens. But to render this position of the sun's 

 centre, and the means of observing it intelligible, it will be 

 necessary to consider the apparent diurnal motion of the heavens 

 under a much more general point of view. 



21. If we suppose an observer to stand with his back to the 

 north, looking to the south, and consequently having the east 

 upon his left, and the west upon his right, the sky being supposed 

 to be cloudless for a day and a night, a remarkable spectacle will 

 be presented to his view, the imposing grandeur of which con- 

 tinues to excite our admiration in spite of the familiarity which 

 is produced by its never-ceasing presence. 



The celestial vault presents the appearance of a vast hollow 

 sphere, one half of which only is presented at any one moment to 

 our view, the base of this visible hemisphere being the plane of 

 the horizon, in the centre of which we stand. This hollow sphere 

 appears to have a motion of rotation round a certain diameter as 

 an axis, carrying with it as it revolves the countless objects, stars, 

 planets, sun, and moon, which appear in various positions upon 

 its stupendous concave surface. Standing in the position here 

 described the sphere seems to revolve from left to right round an 

 axis inclined to the horizon in a vertical plane, directed north and 

 south. This apparent motion causes all the celestial objects to 

 rise in succession on the left, that is on the east, and gradually 

 rising they approach to and pass the vertical plane directed north 

 and south, and after passing it, they descend upon the right, that 

 is on the west, and in fine disappear below the horizon. 



22. This diurnal motion of the celestial sphere is characterised 

 by the most rigorous and absolute uniformity and constancy. It 

 is never faster, never slower, and never stops. It has continued 

 thus to move from time immemorial, and according to all appear- 

 ance, and subject to the existing laws of nature, will continue so 

 to move as long as the globe of the earth endures. 



23. Such constancy and uniformity, combined with the fact 

 that it is universally observable, would render such an apparent 

 motion eminently fitted as a measure of time. Nevertheless as 



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