Mr Hope on Wood Pamng. 255 



the end of three months ; and at the end of the eighteen 

 months about double what the vertical sustained. The sur- 

 face was very much like the preceding, but the soft fibres had 

 suffered more abrasion, and the resinous were separating into 

 threads nearly Jth of an inch. 



5. The blocks with the fibres at 30 degrees lost more in 

 one month than the vertical did in six ; and at the end of the 

 eighteen months Aths more than the vertical. The surface 

 was similar to the last, but to a greater extent. 



6. The block with the fibres leaning at 15 degrees, lost as 

 much in one month as the vertical did in ten ; and in eighteen 

 months full f ths of an inch, being three times more than the 

 vertical. In proportion to the angle, the surface was getting 

 more unequal, sufi^ering greater abrasion, the threads becom- 

 ing longer and irregular, and the general appearance shewing 

 that destruction was making rapid progress. 



7. The last to be noticed are blocks with the fibres hori- 

 zontal. For the first month the wear was equal to fifteen 

 months of the vertical, and in eighteen months they lost about 

 half an inch. The fibres were completely separated to a con- 

 siderable depth, and the surface had the appearance of a Heap 

 of broken strings. 



II. On the Durability of Wood as a Material for Paving. 



It seems indeed strange, that such incompressible and du- 

 rable substances as basalt and granite should be more sub- 

 ject to wear, with the same amount of traffic, than wood with 

 the fibre presented to the pressure and percussion. The 

 former, however, when acted on by the wheels and horses* 

 shoes, resist the pressure and percussion, and thereby have 

 their particles abraded into a very minute sand ; and the iron 

 is also subjected to a diminution in proportion to the hardness 

 of the stone. 



On the other hand, wood, from its elasticity, yields to the 

 pressure, and permits the weight to pass over it without any 

 sensible injury to either the iron or wood. 



A reference to the table will, however, shew the amount 

 of wear wood and granite sustained with the same traffic. 

 The first column will shew that wood lost l-8th of an inch. 



