NOTES 



NOTE 7, p. 79. 



95 



THE RESISTING FORCE ON A SPHERE MOVING ROUND 

 THE SUN AND RADIATING R PER SQ. CM. PER. SECOND 

 AND THE REDUCTION OF ITS ORBIT ROUND THE SUN 

 THE DOPPLER EMISSION EFFECT 



The investigation 1 is divided into three parts : (i) The 

 pressure on a very small area moving along its own 

 normal; (2) the tangential stress on a very small area 

 moving in its own plane; (3) the application of (i) and 

 (2) to a moving sphere 



The principle of the investigation for (i) and (2) con- 

 sists in rinding the momentum in the space between two 

 hemispherical surfaces containing the disturbance emitted 

 in a short time which we may without loss of precision 

 take as the unit time. The resultant of this momentum 

 reversed is the pressure on the area at the time of emission. 

 The stream of energy is normal to the hemispherical 

 surfaces, and we may therefore apply the normal stream 

 method of Note 2, which gives the momentum density 



1 An investigation of the Doppler emission effect was given by 

 the author in Phil. Trans. , 202, 1903, p. 546, but, as pointed out in a 

 note on p. 550, the result obtained was double the true value. The 

 method here given appears to be more direct and satisfactory. 



