IO2 PRESSURE OF LIGHT 



S = 175 x io 6 ; V = 3 x io 10 we obtain as the diminu- 

 tion of r in one second 



IO 3 



The diminution in one year one revolution at distance 

 b is obtained by multiplying by 31-5 x io 6 the value of 

 a year in seconds, and we get 



820 metres. 



If we suppose that the orbit remains so nearly circular 

 that we can use the equation 



_ 

 dt ~ ap V 2 



let us integrate from / = o to / = / and r = b to r = r? 

 Then 



If r t is the radius of the sun, r^/fl may be neglected, and 

 the time taken to reach the sun is 



V 2 

 -*1F 



Dividing by 31*5 x io 6 and using the values a = i, 

 p = 5-5 as before 



/ = 90,000,000 years. 



The time is proportional to ap, so that for a sphere 

 radius o'ooi cm. and of density 5*5 



/ = 90,000 years. 



If the density is that of water these times are reduced 

 respectively to 16,000,000 and 16,000 years. 



The methods here adopted are obviously at the best 

 approximate, but the diminution at the distance of the 

 Earth in a single year agrees with that found from the 



