APPENDIX A 



APPENDIX A 



APPARATUS FOR MEASURING THE AMOUNT OF THE RESISTANCE TO 



IMPACT. 



A square iron frame having a diagonal bar running across it is 

 fixed upon a pillar of sufficient rigidity to resist vibration. A clamp 

 to hold the test piece of wood slides upon the diagonal bar, and is 

 made adjustable by means of three screws so that the cross (trans- 

 verse) section of the wood can be brought precisely to an angle 

 of 45 to the vertical. The diagonal bar is graduated to permit 

 of a movement through a definite space. At a distance of one metre 

 above the wood a small funnel is fixed through which a small steel 

 ball weighing 10 grammes can be dropped upon the wood. At the 

 side of the frame is a strip of brass which is fixed just 25 era. from 

 the point struck by the ball and a piece of squared paper marked 

 at a point cut by a horizontal line drawn from the striking point 

 (for zero) is placed upon it. Over this a typerwriter ribbon is lightly 

 stretched. The ball rebounding from the surface of the wood will 

 strike the ribbon and leave a blue spot upon the paper at a point 

 which will vary according to the amount of force absorbed by the 

 wood. The harder the wood the nearer the mark will be to the 

 horizontal, and on the contrary the trajectory of the ball will sink 

 in proportion to the softness of the wood. As the zones of the annual 

 rings will vary in their resistance, it will be necessary to slide the 

 clamp for a short distance (say 5 mm.) for a series of (say ten) 

 shots ; this will give a fair average for the alternating hard and 

 soft parts of any wood. 



It will be seen that providing the conditions are complied with, 

 similar results may be obtained by different observers, as nothing 

 will depend upon their personal idiosyncrasies. 



In addition to the apparatus described above, a small spirit level 

 of the kind used by photographers fixed in one of the short sides of 

 a right-angled triangular prism is needed in order to adjust the sur- 

 face of the wood to the proper angle, and a small plummet to be 

 suspended from within the tube of the funnel is requisite to insure 

 the latter being exactly over the desired point upon the surface oi 

 the wood. 



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