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VIII. — On Impact. By Professor Tait. (With a Plate.) 



(Revised November 8th, 1890.) 



The present inquiry is closely connected with some of the phenomena presented in 

 golf: — especially the fact that a ball can be "jerked" nearly as far as it can be "driven." 

 For this, in itself, furnishes a complete proof that the duration of the impact is 

 exceedingly short. But it does not appear that any accurate determination of the 

 duration can be made in this way. Measurements, even of a rude kind, are impracticable 

 under the circumstances. 



In 1887 I made a number of preliminary experiments with the view of devising a 

 form of apparatus which should trace a permanent record of the circumstances of impact. 

 I found that it was necessary that one of the two impinging bodies should be fixed : — at 

 least if the apparatus were to be at once simple and manageable. This arrangement gives, 

 of course, a result not directly comparable with the behaviour of a golf-ball. For pressure 

 is applied to one side only, both of ball and of club ; but when one of two impinging 

 bodies is fixed it is virtually struck simultaneously on both sides. Even with the altered 

 conditions, however, the inquiry seemed to be worth pursuing. I determined to operate, 

 at least at first, on cylinders of the elastic material ; so fixed that considerable speed 

 might be employed, while the details of several successive rebounds could be recorded. 

 It is not at all likely that this will be found to be the best form for the distorted body ; 

 but it was adopted as, in many respects, convenient for preliminary work. For the main 

 object of the experiments was to gain some information about a subject which seems to 

 have been left almost entirely unexplored ; and it is only by trial that we can hope to 

 discover the best arrangement. Messrs Herbertson and Turnbull, who were at the 

 time Neil-Arnott Scholars, and working in my Laboratory, rendered me great assistance 

 in these preliminary trials, whose result was the construction of a first rude apparatus on 

 the following plan. 



A brick-shaped block of hard wood was dropped endwise from a measured height 

 upon a short cylinder of cork, vulcanized india-rubber, gutta-percha, &c, which was 

 imbedded to half its length in a mass of lead, firmly cemented to an asphalt floor. The 

 block slid freely between guide-rails, precisely like the axe of a guillotine. In front of 

 the block was a massive fly-wheel, fitted on one end of its axle, and carrying a large 

 hoard (planed true) on which was stretched, by means of drawing pins, a sheet of 

 cartridge-paper. The sheet was thus made to revolve in its own plane. A pencil, project- 

 ing from the block, was caused by a spring to press lightly upon the paper ; and it was 

 adjusted so that its plane of motion passed as exactly as possible through the axis of the 

 paper disc. To prevent breakage of the pencil on the edge of the disc, it was pushed 



VOL. XXXVI. PART I. (NO. 8). 2 M 



