344 METEOROLOGY. 



diurnal intensity, in Section IV, would be altered as by tbe multi- 

 plier 1 — 0.11 in summer, and 1 -{- 0.11 in winter. This would 

 diminish the midsummer intensity by about 9°, and increase the 

 midwinter intensity by 3° or 4° ; the temperature of spring and 

 autumn being nearly unchanged. But this does not appear to be of 

 itself adequate to the geological effects in question. 



It is not our purpose here, to enter into the inquiry, whether the 

 atmosphere was once more dense than now, whether the earth's 

 axis had once a different inclination to the- orbit, or the sun a 

 greater emissive power of heat and light. Neither shall we at- 

 tempt to speculate upon the primitive heat of the earth nor of 

 planetary space, nor of the supposed connection of terrestrial heat and 

 magnetism ; nor inquire how far the existence of coal fields in this 

 latitude, of fossils, and other geological remains have depended upon 

 existing causes. The preceding discussion seems to prove simply that, 

 under the present system of physical astronomy, the sun's intensity 

 could never have been very greatly different from what is manifested 

 upon the earth at the present day. The causes of notable geological 

 changes must he other than the relative position of the sun and earth, under 

 their present laws of motion. 



If we extend our view, however, to the general movement of the Sun 

 and Planets in space, we find here a possible cause for the remarkable 

 changes of temperature traced in the geological periods. For, as 

 Poisson conjectured, Theorie de la Chalezcr, p. 438, the phenomena 

 may depend upon an inequality of temperature in the regions of space, 

 through which the earth has passed. According to a calculation quo- 

 ted by Prof. Nichol, the velocity of this great movement is six times 

 greater than that of the earth in its orbit, or about 400,000 miles per 

 hour. 



In this motion, continued for countless ages, the earth may have 

 traversed the vicinity of some one of the fixed stars, which are suns, 

 whose radiance would tend to efface the vicissitudes of summer and 

 winter, if not of day and night, with a more warm and equable cli- 

 mate. This may have produced those luxuriant forests, of which the 

 present coal fields are the remains; and thus the existence of coal 

 mines in Disco, and other Arctic islands, may be accounted tor. If no 

 similar traces exist in the Antarctic zone, the presumption will be 

 strengthened, that the North Pole was presented more directly to the 

 rays of such illuminating sun or star. Indeed, by this position, all 

 possibility of conflict with Neptune, and the other planets which lie 

 nearly in the plane of the ecliptic, were avoided. 



The descrijttion of such period, with strange constellations and 

 another sun gleaming in the firmament, their mysterious effects upon 

 the growth of animals and vegetation, their untold vicis^itudes of 

 light, shadow and eclipse, belong to the romance of astronomy and 

 geology. As in the ancient tradition described by Virgil in the sixth 

 Eclogue: — 



Jamqiie novum terrte stupeant lure^cere Foleni : 

 Allius atqne cadaiit sulimutis tiubibus inibies : 

 Incipiarit silvcG quarn primuni surgere, quumqua 

 Rara per igiiolos errent aniinalia monies. 



