158 Mr. Knight on the different qualities, &c. 
winter-felled tree 145 grains ; and I found that each sub- 
stance permanently retained moisture nearly in the same pro- 
portion that it absorbed it. The alburnum of the oak, as of 
other trees, therefore, undergoes some change of properties 
in the spring; and I do not entertain any doubt but that, in 
all cases in which it is expedient to give durability to that 
substance, much advantage may be obtained by taking off the 
bark in spring, and suffering the trees to stand till winter. 
The durability of the alburnum of large oak-trees of British 
growth is not, however, generally an object of much conse- 
quence ; because it almost always lies wholly exterior to the 
heart wood ; but in the oak timber, which is imported from 
the North of Europe, the alburnum and heart wood are very 
often intermixed, the growth of ten or a dozen years, or more, 
of alburnum and heart wood composing, in alternate layers 
of unequal depth, the whole body of the tree; and the value 
of the timber of such trees, is probably much affected by the 
season of felling. 
Many experiments, similar to the preceding, were made 
upon the heart wood, in which I found the disposition to 
absorb moisture, somewhat greater in that of the spring-felled, 
than in that of the winter-felled tree ; and I scarcely entertain 
any doubt but that the winter-felled heart wood is the best, 
and most durable ; but I do not think any conclusion can 
safely be drawn till the heart wood of many trees has been 
subjected to experiment ; and therefore, as I have no evidence 
to offer which is in any degree conclusive, I shall not at pre- 
sent trespass farther upon the attention of the Society. 
Downton, 
March zg, 1820. 
