Sentence:  Whipple ( 1955 ) extends the effects to include the solar <WSD>corpuscular</WSD> radiation pressure , which increases both the minimum particle size and the drag . 
Meaning of the word marked with <WSD> tags:  a stream of atomic or subatomic particles that may be charged positively (e.g. alpha particles) or negatively (e.g. beta particles) or not at all (e.g. neutrons)