Intelligence and Miscellaneous Articles. 393 



For the body in question F represents a characteristic constant, 

 which is independent of the distance from the sun, since P and A 

 depend in the same way on this distance. 



Replacing P and A in (4) by their numerical magnitudes (2) 

 and (3), we obtain approximately 



F=l-^ (5) 



re 



It is clear from this that for all bodies in which 3^1 and r > 10 m., 

 the deviations from Newton's law must lie below the errors of 

 observation of the most accurate measurements. 



The smaller r is chosen, the more prominent does the repulsive 

 force of the sun become. If we pass over to comets' tails, which 

 are known to consist principally of gaseous hydrocarbons *, they 

 represent for us the individual molecules in which, according to 

 Exnerf, 3<10 and r<10 _8 cm. Our formula (5) cannot be in 

 strictness applied to this case, since the individual molecules are not 

 absolutely black bodies, and their radii are very small compared with 

 the wave-length of the incident radiation ; formula (5), however, 

 allows us to suppose that in this case the repulsive force may be 

 several times greater than the attractive, that this may be of 

 different magnitudes for different vapours, and decreases in inverse 

 proportion to the square of the distance from the sun. Bredichin $ 

 has calculated from the curvatures of the tails of forty comets, by 

 Bessel's method, the repulsive force which the sun exerts on 

 various substances forming the tails, and has found three values 

 17*5, 1*1, and 0*2 ; these values can without straining be referred 

 to the mechanical action of the radiation, without, like Zollner §, 

 having recourse to the assumption of an electrostatic charge on the 

 sun. 



It maybe observed that Faye || has already expressed the opinion 

 that the repulsive force of the sun is to be sought in its radiation. 



We now turn to general considerations : any body, the tem- 

 perature of which is different from the absolute null point, 

 radiates and exerts on an adjacent body a repulsion by radiation 

 besides the Newtonian attraction. 



If, in place of the sun, we have a spherical body the radius of 

 which is E centimetres, and the density A, and if 1 square 

 centimetre of its surface radiates Q gramme-calories in one second, 

 we can treat this case based on the results found for the sun, 

 taking into consideration that 



* Schemer, 8})ectralanalyse der Gestirne, pt. iii. chapter o ; Leipzig, 

 1890. 



t Wied. Beibldtter, vol. ix. p. 714 (1885). 



\ Revision des valeurs numeriques de la force repulsive ; Leipzig, 1885. 



§ Ueber die Natur der Kometen ; Leipzig, 1872. 



I| Cot7ipt. rend. vol. xciii. pp. 11 and 302 (1881). 



