INTENSITY OF SUN'S HEAT AND LIGHT. 41 



shall we attempt 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 materially different from what is manifested upon 

 the earth at the present day. The causes of notable geological changes must be 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 Chaleur, 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 quoted 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 climate. 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 for. 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, was avoided. 



The description 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 vicissitudes 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 : — 



' Jamque novum terra? stupeant lucescere solem : 



Altius atque cadant submotis nubibus imbres : 



Incipiant silva? quatn primum surgere, quumque 



Rara per ignotos errent animalia montes. 



It is evident that, in receding from the sphere of intensity of such star, as a 

 comet from the sun, the earth's annual temperature would very slowly decrease in 

 process of time, according to the temperature of the space traversed. And, at a 

 remote distance from the stars, the temperature of space ought to remain stationary; 

 as the mean annual temperature of the earth has remained for at least two thousand 

 years past, and without doubt will so continue for ages to come. 



