in the receiver h is removed about every three hours. As 

 in all hardness tests there is no absolute standard ; we have 

 no unit for expressing the resistance to abrasion except by 

 comparing the relative behaviour of materials tested under 

 similar conditions. If we decide upon some material as a 

 standard, then it is possible in give the hardness of other 

 materials as a ratio of the hardness of the standard in the 

 same way as the specific gravity of a material is expressed 

 in regard to that of water as a standard. We therefore 

 have to decide on some material to be used as a stan lard 

 for hardness. For this purpose North Coast Blackbutt has 

 been decided upon, and the hardness of all the other timbers 

 are given in terms of this standard. 



As in " the holding power of nails and dog-spikes " and 

 in the Brinell Ball Test, there are three different direc- 

 tions in which the timber can be tested namely, those 

 marked a, b, c, in Fig. 1. 



d shows a wood block. 



