In one experiment, to prove that colour was caused by pressure on the eye, Newton slid a darning needle around the side of his eye until he could poke at its rear side, dispassionately noting "white, darke & coloured circles" so long as he kept stirring with "ye bodkin."

Use of the term "darning needle" in the above quote is questionable. It gives the impression Newton was poking a sharp needle in his eye. However, he calls it a "bodkin" which is a needle with a rounded, not sharp, point. Bodkins are commonly used for sewing ribbon into eyelet lace. Click for pic.