Bram.—On the Building Materials of Otago. 139 
The amount of moisture contained in the ordinary English timbers is 
shewn by the following table : 
In pounds weight | In pounds weight 
per cubic foot.  |per cubic foot, when 
Oak " 77 52 
sh 65 50 
Beech dm 65 50 
ae vt c ue vA "n 70 48 
Fir a "m s ss ne as 54 to 74 81 to 41 
The ultimate transverse shrinkage in the seasoning of boards twelve 
inches square and half an inch thick, is found to be for oak, +1; the breadth ; 
Riga fir, 4, ; Virginia pine, +7 ; larch, 4, ; elm, 44 ; kauri, 44. 
Decay and Preservation—The causes of decay in timber are of three 
kinds :—1st. Chemical decay—a natural decomposition by the action of the 
air and moisture; 2nd. Vegetable decay or dryrot, a decomposition that takes 
place through the growth of fungi ; and 8rd. Animal decay, waste by the de- 
struction caused by worms and insects. The first of these is to all intents and 
purposes aslow combustion effected by the acids ofthe atmosphere, and greatly 
accelerated by changes from wet to dry. Most timbers will last a long time 
if kept constantly wet or constantly dry in an equable temperature, but 
the best only will stand exposure to severe alternations from wet to dry ; 
the most trying situation for timber in this respect is in posts in the ground, 
decay always attacks it first at the surface, between wet and dry. I am not 
aware of any eure for this natural decay ; charring, painting or tarring will 
retard its progress, but the only safe course is the use of a durable timber 
well seasoned. In connection with this I may notice a practice that exists 
among our settlers of inverting posts when putting them in the ground to 
inerease their durability ; like the lunar influence already noticed this was 
long thought to be only an imaginary benefit, but lately the matter has 
become an established fact. Experiments made in England on oak posts 
from the same tree showed those put in the ground with the top up- 
wards as they grew, to be rotten in twelve years, while their neighbours 
that were inverted showed no symptoms of decay in sixteen years. This is 
explained by assuming that the capillary tubes are provided with valves 
which open upwards, on inverting the post these valves oppose the rising of 
moisture. 
The relative durability of the timbers in common use in England has 
been ascertained by inserting pieces 2§ inches square into the ground; they 
decayed in the following order :— 
Lime, American Birch, Alder, and Aspen  ... ue 3 years. 
Willow, Horse Chestnut, and Plane ... ben ce 4 
LE] 
