104 Professor E. F. Nichols on Radiation Pressure. [May 12, 



radiation in a given direction receives a backward pressure from its 

 own emission. Professor Pojnting has shown that when a hot body 

 radiating equally in all directions is in motion, the intensity of its 

 radiation will, in accordance with Doppler's principle, be sHghtly 

 greater in front than behind ; hence the radiation pressures fore and 

 aft will no longer balance, and there will be a resultant pressure 

 tending to retard the body's motion. 



If such a body should retain its temperature long enough it must 

 inevitably come to rest, and not keep moving on for ever as we have 

 previously beUeved. 



[E. F. N.] 



