256 Mr Hope on Wood Paving, 



but more from compression than abrasion ; and the last column 

 will shew that granite sets lost 7-32(ls of an inch from abrasion 

 alone, — which proves that the elasticity of wood is that which 

 renders it durable and applicable for paving ; and that the 

 non-elastic property of stone is the cause of its inferior dura- 

 bility. 



III. On the EJicicncy of Wood for Paving, when necessarily 

 subjected to Wet and Dry Weather, 



It is now sufficiently established, by men of maritime ex- 

 perience and ship-builders, that those parts of a vessel which 

 are constantly exposed to the water, are never found to be the 

 least affected, while other parts of the same vessel are under- 

 going rapid decay ; and that decay is even arrested when it 

 reaches the same seasoned parts. 



Wood blocks in pavement may thus be said to be quite 

 exempt from the probability of decay, even although they 

 should be perfectly dry when laid down (a condition to be 

 particularly recommended). They are placed on a humid, or 

 what will soon become humid, substratum, closely packed to 

 each other, and totally excluded from atmospheric influence, 

 saving the surface. In wet weather they absorb as much 

 moisture as they can contain, which renders them more ad- 

 hesive and compact ; and from which moisture they are never 

 after totally free, even in the dryest weather ; for wood 

 being a bad conductor of caloric, any variation of the atmo- 

 sphere has little effect on the blocks, or the surface exposed 

 to it. 



To prove this, I weighed a number of the blocks when laid 

 down ; and, after having been in use till properly moistened, 

 had them taken up and reweighed, when I found that they 

 had gained by moisture 4|th ounces. After a long continuance 

 of dry weather, I had them again taken up and weighed, and 

 found that they were still moist, having lost only Ifth ounce. 

 I also split some of the blocks, and found that they were 

 moist to the core, except about an inch from the surface, but 

 regained that moisture towards the evening. I tiied this ex- 

 periment frequently, with similar results. The small differ- 

 ence in the size of the blocks, under various degrees of tem- 



