I2 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
I give below, in a Table, Bauschinger’s results, reduced to a 
ro per cent. dryness, for the same qualities of timber as those for 
which I have given the tensile results. 
Summer felled. 
Scots Pine, . : ‘ 5310 lbs. per square inch. 
Norway Spruce, . : A779: 9 - 
Winter felled. 
scots Pine,.. ; : 7167 lbs. per square inch. 
Norway Spruce, . : 5600 ,, ss ” 
Professor Lanza made an exhaustive investigation into the 
strength of a large number of full-sized specimens of American 
timber, from 7 inches to ro inches in diameter, and about 12 feet 
long ; these all collapsed by pure compression, and the average 
results are given in the Table below :— 
Max. Min. Mean. 
Yellow Pine(Pinus echinata), 4720 3920 4370lbs. persquareinch. 
Old and seasoned White \ 5197 3065 4480 
Oak (Quercus alba), : 7 @ 5. 
Professor Johnson, in the experiments for the American 
Forest Board, used compressive specimens 8 inches long and 
4 inches square in cross section, these specimens being cut from 
the ends of other specimens, which had been used as beams. 
For the purpose of this lecture, I tested a couple of specimens, 
one of beech and one of white (Weymouth) pine (Pinus Strobus). 
In all such tests there is a tendency to give way by shear, especially 
near one end, that is to say, the direct compressive force when 
resolved on a plane inclined to the axis of the specimen, produces 
a shear in this plane which soon exceeds the maximum shearing 
strength of the material, and thus a short strut in wood tends 
rather to give way by shear than by direct compression. The 
white (Weymouth) pine specimens only carried 2°31 tons per 
square inch of direct compression when shear set in. 
Professor Johnson also agreed with Bauschinger that com- 
pression experiments were easier to carry out, and were the most 
valuable of all tests; he advised a factor of safety of 8 for dry 
timber and of 5 for green timber, when designing timber struts. 
