CULTURE OF THE GRAPE. 191 



but those in the blackened part of the wall were much 

 finer than those on the plain part. This year the success 

 of my experiment has been complete. The weight of 

 fine grapes gathered from the blackened part of the wall 

 was twenty pounds and ten ounces; while the plain part 

 yielded only seven pounds and one ounce, being little 

 more than one-third of the other. The fruit on the black- 

 ened part of the wall was also much finer, the bunches 

 were larger and better ripened, than on the other half: 

 the wood of the vine was likewise stronger, and more 

 covered with leaves, on the blackened part. It is a gen- 

 erally known fact, that a black, unpolished surface ab- 

 sorbs more rapidly than other colors the sun's rays, and 

 thereby becomes sooner heated. It is equally well known, 

 that surfaces which absorb heat more quickly part with 

 it more easily when the source of heat is withdrawn, and 

 cool quicker. In the summer-time, when the days are 

 long, the wall will be more intensely heated under .the 

 blackened surface; and, the night (or time of cooling) 

 being short, it may not have returned to the temperature 

 of the air before it is again subjected to an increase of 

 heat. If the time of cooling were long enough, that part 

 of the wall under the blackened surface might become 



