Mr Jaffers, the constable, now arrived, and was quite surprised to find that he had to arrest a man without a head. But Jaffers was not easily prevented from doing his duty. If a magistrate’s warrant ordered a person’s arrest, then that person had to be arrested, with or without his head.
     There followed a remarkable scene as the policeman tried to get hold of a man who was becoming more and more invisible as he threw off one garment after another. Finally a shirt flew into the air, and the constable found himself struggling with someone he could not see at all. Some people tried to help him, but found themselves hit by blows that seemed to come from nowhere.

     In the end Jaffers was knocked unconscious as he made a last attempt to hold on to the unseen scientist.

     There were nervous, excited cries of “Hold him!” But this was easier said than done. Griffin had shaken himself free, and no one knew where to lay hands on him.
Mr Jaffers, the local policeman, was taken aback when he realised he had to arrest a man who had no head. But Jaffers still wanted to fulfil his job since he knew the magistrate wanted him to arrest the individual, regardless of whether he had a head or not.

The entire thing was reaching its breaking point. The scientist threw away his garments whenever the cop sought to capture him. In addition, when he throws one dress after another, he becomes more invisible. Griffin finally became invisible after removing his shirt, and Jaffers sought to capture a man who had become entirely disappeared.

People who attempted to assist Jaffers were also struggling as strikes from nowhere hit them. The invisible guy punched Jaffers and became unconscious as the constable made his final attempt to grab the invisible man. Everyone yelled "hold him" repeatedly, but Griffin had gotten away from them, and no one knew how to grab him.
Meanings of the difficult words:
Headless Without a head
Unconscious Not conscious
Garment A piece of clothing
National Council of Educational Research and Training (2007). Footprints without Feet - H.G. Wells(pp. 26-31). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.