BADIATING HEAT. 41 



are affected by the different positions of the sun or moon, 

 notwithstanding the latter's contiguity to the earth. The 

 magnetic polarity of the earth exhibits no variations that can 

 be referred to the sun, or which perceptibly affect the pre- 

 cession of the equinoxes. 23 The remarkable rotatory or oscil- 

 latory motion of the radiating cone of light of Halley's 

 comet, which Bessel observed from the 12th to the 22nd of 

 October, 1835, and endeavoured to explain, led this great 

 astronomer to the conviction that there existed a polar force, 

 " whose action differed considerably from gravitation or the 

 ordinary attracting force of the sun ; since those portions of 

 the comet which constitute the tail are acted upon by a repulsive 

 force proceeding from the body of the sun.' 1 ' 74 ' The splendid 

 comet of 1744, which was described by Heinsius, led my 

 deceased friend to similar conjectures. 



The actions of radiating heat in the regions of space are 

 regarded as less problematical than electro-magnetic pheno- 

 mena. According to Fourier and Poisson, the temperature 

 of the regions of space is the result of radiation of heat from 

 the sun and all astral bodies, minus the quantity lost by 

 absorption in traversing the regions of space filled with ether. 2 * 

 Frequent mention is made in antiquity by the Greek and 

 Roman 26 writers of this stellar heat; not only because, from 



23 See Bessel, in Schumacher's Astr. Nachr.,\)d. xiii. 1836, 

 no. 300, s. 201. 



24 Bessel, op. ciL, s. 186-192, 229. 



25 Fourier, Theorie analytique de la Chaleur, 1822, p. ix. 

 (Annales de Chimie et de Physique, torn. iii. 1816, p. 350; 

 torn. iv. 1817, p. 128 ; torn. vi. 1817, p. 259 ; torn. xiii. 1820, 

 p. 418). Poisson, in his Theorie mathematique de la Chaleur 

 ( 196, p. 436, 200, p. 447, and 228, p. 521), attempts 

 to give the numerical estimates of the stellar heat (chaleur 

 stellaire} lost by absorption in the ether of the regions of 

 space. 



* On the heating power of the stars, see Aristot. de Meteor, 



