Sentence:  <WSD>Further</WSD> , the corpuscular radiation , i.e. , the solar wind protons , must sputter away the surface atoms of the dust and cause a slow diminution in size , with a resultant increase in both the Poynting-Robertson effect and the ratio of the repulsive force to the gravitational force . 
Meaning of the word marked with <WSD> tags:  in addition or furthermore; further, they should be here already"