Drawings, Microscopic structures observed in frozen urine and ice by Robert Hooke Illustrations showing the structures observed in frozen urine by Robert Hooke and communicated to the meeting of the Royal Society on 17 December 1662. Fig. 1 shows the branching structures on the surface of frozen urine; fig. 6 shows the parallel lines observed on flakes of ice frozen on the top of water. Writing accompanying the drawings reads: ''This figure is to be drawn on ye side of ye paper concerning ye Figures frozen in Urine, marked by Mr Hook'. Subject: Natural Philosophy, Chemistry 10 December 1662