394 Intelligence and Miscellaneous Articles. 



the sun's radius E ==7 . 10 10 em. 



„ „ density A =l*4. 



„ radiation of 1 square cm. of 



its surface in 1 second . . . Q = 2000 gramme-calories*. 



If we denote by s the ratio of the repulsive force of the radiation 

 to the Newtonian force of attraction, we may contend that s is 

 direct] v proportional to Q, inversely proportional to A and also 

 toEf. 



For the sun we have from (5) the value s : 



__10-4 

 Hence for any other body we have 



°Q,4B' (6) 



or, replacing the magnitudes s , Q , A , and E by the corre- 

 sponding numerical values, we obtain approximately 



s=5-§- .10 3 (7) 



The resultant K of the attraction and repulsion is 



K=l-s=l-5 Q .10 3 (8) 



?3EA v } 



Christiansen % found for a black body that radiates Q' gramme- 

 calories in a second at 0° C. from 1 sq. centimetre of its surface, 

 approximately 



Q'= (1-21 . 10- 12 j (274) 4 =0-004 gramme-calorie. 



Hence the force K' with which a spherical absolutely black 

 body, whose radius is E cm., density A, and temperature 0°, attracts 

 another spherical body in space whose radius is r cm. and density c, 

 is furnished by the expression 



K'-l--f° (9) 



Accordingly, two bodies whose temperatures are 0°, radii H=r.r 

 = 2mm., and densities A=£=10, would neither attract nor repel 

 each other in space. If we assume that the radii of the bodies 



* If at the distance of the earth p=15 . 10 12 centim. the quantity of 

 heat c/60 = 0-05 gramme-calorie falls on 1 square centim., then 1 square 

 centim. of the sun's surface, which is at a distance of E = 7 . 10 10 centim. 

 from the centre, radiates the quantity of heat Q =0*05 (/3/E ) 2 = 2000 

 gramme- calories in one second. 



t Since the attractive force of the mass is proportional to E 3 , and the 

 repulsive force of radiation to E 2 . 



X Wied. Ann. vol. xix. p. 272 (1883). 



