We have picked on c (i.e., tangential to the anmiiil rings) 

 as that direction in which we test the timber for the 

 standard determination of the resistance to abrasion. The 

 sand used in these tests was supplied by the Emu Plains 

 Road Metal and Gravel Company, and lias all been passed 

 through a sieve of 900 meshes to the square inch. The 

 specimens are all cut to a size 3" x 3" x 1 ", and are weighed 

 to the nearest grain before being subjected to the test. 



When the tests are over, the specimens are immediately 

 weighed again and the loss of weight noted. It is necessary 

 that the weighing should be done not long before, and soon 

 as possible after the test, as, owing to the hygroscopic 

 properties of the timber, we are likely to get a change in 

 weight on account of the timber absorbing or giving off 

 moisture. Having noted the weight thus abraded, we must 

 divide by the weight per cubic inch of the timber which 

 will give us the volume in cubic inches abraded. We 

 multiply this by a constant (10 3 =1000) so as to bring the 

 result to a convenient size, and we can follow the same 

 procedure for each timber thus obtaining a series of num- 

 bers. We could write the numbers down as the hardness 

 numbers of the various timbers, provided that the conditions 

 of testing were always the same. 



The greatest discrepancy in the constancy of the con- 

 ditions is likely to occur in the case of the sand as we can- 

 not always be certain of getting sand of the same quality. 

 It might, for example, contain more quartz particles or be 

 less finely divided than the last lot, which would tend to 

 greatly alter the results of the two series, though each 

 timber in either series would be perfectly comparable with 

 any other timber in that series of tests. And so we can 

 by using a piece of the standard timber in each series of 

 tests reduce both series to a common basis and compare 

 them one with the other, irrespective of what the con- 



