Mr Hope on Wood Paving. 257 



peraturc, also bears out these experiments. The medium 

 variation I could discover in their volume was .057, which I 

 attributed to the loss or gain of moisture ; and this trifling 

 diffxjrence of volume did not affect the adhesion of the blocks, 

 or the general structure, in consequence of the moisture they 

 retained in dry weather still maintaining an excess of volume 

 over the dry state in which they were originally laid down. 



To discover if it was from the exclusion of atmospheric in- 

 fluence that the moisture was retained, and occasioned their 

 limited expansion and contraction, and not any peculiarity of 

 the wood of the precise blocks used, I found that, in wet 

 weather, blocks, when taken out and kept singly, expanded 

 as freely as those used for comparison ; and when they became 

 the exact weight they were when taken out in dry weather, 

 their volume was proportionally greater ; and when kept till 

 perfectly dry, they were reduced to their original dimensions. 



I also found that the moisture contributed much towards 

 imparting additional strength to the fibres of the wood, and 

 rendering it more capable of resisting pressure and abrasion, 

 besides preserving it from dry rot. 



IV. Having glanced at the durability of wood under wet 

 and dry weather, the next thing to be considered is the eff*ect 

 which frost has upon it. 



In Russia, where the climate is so rigorous, frost might be 

 supposed to be an insuperable objection ; but when we find 

 that it was in that country, some centuries ago, where wood 

 paving was first adopted, and that a system not inferior to 

 what is practised here, has been there for many years in gene- 

 ral use, we may consider that, in the mild climate of Britain^ 

 where frost is neither severe nor of long duration, it can only 

 be of trifling consequence. 



In Russia it is admitted that frost has a deleterious effect 

 on the wood, — to counteract which, they give it an annual 

 coating of tar covered with sand, which, with other advantages, 

 obviates any excess of slipperyness. 



1 found that the surface coated with common varnish and 

 sand was highly beneficial. It preserved a more uniform tem- 

 perature (although, as I have stated, the want of this greater 



