Unpublished extract, 'On approach caused by vibration' by Frederick Guthrie This is an unpublished section of a paper by Guthrie which was abstracted in volume 18 of the Proceedings of the Royal Society as 'On approach caused by vibration'. In the paper, Guthrie observes that when a vibrating tuning fork is held close to a piece of cardboard, the latter has a tendency to approach the fork. Starting from this experiment, a series of experiments is described having for their object the determination of the cause and conditions of the fundamental observed fact. Annotations in pencil and ink throughout. Subject: Physics 1869