This has recently been interpreted by a few writers as a sarcastic remark directed at Hooke's appearance. Although Hooke was not of particularly short stature, he was of slight build and had been afflicted from his youth with a severe kyphosis. However, at this time Hooke and Newton were on good terms and had exchanged many letters in tones of mutual regard. Only later, when Robert Hooke criticized some of Newton's ideas regarding optics, was Newton so offended that he withdrew from public debate. The two men remained enemies until Hooke's death.