INDEXED. 



THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 





[SIXTH SERIES'J 



APRIL 1905. 



XXXIX. Radiation Pressure. 

 ByJ.K. Poyxtixg, Sc.D., F.R.S.* 



A HUNDRED years ago, when the corpuscular theory 

 held almost universal sway, it would have been much 

 more easy to account for and explain the pressure of light 

 than it is today, when we are all certain that light is a form 

 of wave-motion. Indeed, on the corpuscular theory it was 

 so natural to expect a pressure that numerous attempts were 

 made t in the eighteenth century to detect it. But tho 

 early experimenters had a greatly exaggerated idea of the 

 force they looked for. Even on their own theory it would 

 only have double the value which w r e now know it to possess, 

 and their methods of experiment were utterly inadequate to 

 show so small a quantity. But had these eighteenth-century 

 philosophers been able to command the more refined methods 

 of today, and been able to carry out the great experiments of 

 Lebedew and of Nichols and Hull, and had they further known 

 of the emission of corpuscles revealed to us by the cathode 

 stream and by radioactive bodies, there can be little doubt that 

 Young and Fresnel would have had much greater difficulty 

 in dethroning the corpuscular theory and setting up the wave 

 theory in its place. 



The existence of pressure due to waves, though held by 



* Communicated by the Physical Society; being the Presidential 

 Address, delivered at the Annual General Meeting, February 10, 1905. 



t Some account of these methods is given by Nichols and Hull in 

 u The Pressure due to Radiation/' Proc. Am. Ac. xxxviii. No. 20, p. 559. 

 See also Priestley, u On Vision," p. 385. 



Phil. Man. S. G. Vol. 9. No. 52. April 1 905. 2 D 



