Page:Timber and Timber Trees, Native and Foreign.djvu/86

66 Fir of the same dimensions, as shown in subsequent Tables, might be loaded to 67 tons.

As before stated, I have applied this description of test to a great variety of woods, and it has enabled me to ascertain with tolerable accuracy the amount of strain they will each bear to the square inch of base. The general result of the trials with gradation of lengths confirms, in some degree, the theory of a four-fifths proportion of base to length, and shows it to be at least approximately correct. Therefore, with this data for our guidance, aided by a little practical judgment, there should be no difficulty in determining the scantlings of props and supports for all ordinary purposes.

There is yet another description of test to be noticed, namely, that for ascertaining the elongation of the fibres under certain strains. The experiment was made in one of the royal dockyards upon two pieces of English Oak, each 2 x 2 x 48 inches, and very carefully conducted—note being taken of the elongation in a length of 3 feet; the mean results were found to be as follows, viz.:—