Pleasant Ways in Science. 267 



all stars tell us the same tale, we accept their evidence that 

 our big earth-ball, which at the equator is nearly twenty-five* 

 thousand miles in circumference, turns round its own axis in a 

 little less than twice twelve hours. f Now if we could get a 

 fairy stool to stand upon nothing, above the earth's surface at 

 the equator, and we could sit upon it, and watch the globe 

 spin round, it would in the course of a day and night spread 

 before us its five-and-twenty thousand miles of successive 

 scenery. Great cities with their " cloud capped towers " and 

 " gorgeous palaces," cultivated fields, primeval forests, desert 

 lands, and ocean with its varied shores, would come and vanish 

 like the thoughts and pictures of a wondrous dream. According 

 to this supposition we should be quite still, while every point 

 on the equatorial circle would travel through a space equal to 

 the globe's circumference in its daily journey. As facts go, 

 we are practically still, or move so little in the course of the 

 day that we may be considered so, and the globe takes us 

 round with it in the prodigious tour we have described, not 

 bringing before our eyes a succession of terrestrial scenes, but 

 unfolding the heavens as a scroll, and enabling us to read their 

 glorious characters as successive portions rise to our view in 

 the east and vanish in the west. The earth's velocity of rota- 

 tion at the equator is 1520 feet in a second — rather less than 

 the initial velocity of a rifle-ball. In our latitude it is about 

 820 feet per second. 



In addition to this journey of rotation, we have another 

 one to take, namely, that of revolution round the sun, and this 

 we accomplish at an average rate of sixty- eight thousand and 

 forty miles an hour. 



Thus, two swift motions operate upon us, and we feel them 

 not — only know them by reasoning from facts that afford no evi- 

 dence of them to an uneducated mind. The common eye cannot 

 fail to see the sun, and moon, and stars rise and set. A more 

 watchful eye notices that at different seasons our skies exhibit 

 different groups of stars, in regular and recurring succession. 



* The diameter of the earth is 7925 "604 miles, and its circumference 24,809 

 miles. The circumference of a circle is rather more than three times its diameter, 

 say 3-14159 times. 



t It is not necessary for our present purpose to take into account the effect 

 produced upon the period between two successive advents of any star on the 

 meridian, by the motion of the poles of the earth, which do not constantly point 

 to the same place in the heavens. For explanation of this, the reader can see 

 Sir J. Herschel's Outlines of Astronomy. The difference between a solar day, 

 averaging twenty -four hours, and a sidereal day, must be borne in mind. As the 

 change in the position of the earth's poles is small and slow, and as the stars are 

 too remote for their proper motions to affect the question, we may consider them 

 as fixed points, to which the same meridian returns in equal times. The sun 

 does not appear fixed. It seems to traverse the heavens in its annual motion in 

 a direction opposite to its diurnal motion, so that the latter motion appears 

 slower than the diurnal motion of the stars, and the 6olar day is so much longer. 



