CHAPTER XXX

TIMBER MEASURING

To those who are not practically acquainted with the measuring of home-grown timber the following brief remarks in elucidation of the subject will be useful. It may, however, be well to mention that timber measuring is rather a vexed question, some following what is known as Hoppus’s system, and others advocating that of Horton. The former being that generally in use amongst timber merchants in this country, and consequently of greatest value to the forester, the following details of this system may prove serviceable.

Regarding the timber-measurer’s equipment it may first be necessary to say a few words. This consists of a 66 ft. Chesterman’s tape-line, or instead of this a 5 ft. wooden rod, standard girt-strap, or fine cord, scribing knife, and bent piece of iron, with eye at end for drawing the girt-strap beneath such trees as the arm cannot readily pass under.

For girthing timber a piece of thin whipcord or string is frequently used, but as the elasticity of this varies greatly, and has in many instances led to dispute, a much fairer plan and one that is liable to no abuse is to use the 12 ft. girt-strap, upon which every inch in length is reckoned ¼. As the proper quarter-girth can be seen at a glance on this strap, its adoption will at once remove any chance of trickery, which may be possible in the use of the string and rule.

For entering measurements the most convenient book is that 9 in. by 4 in., with stiff pasteboard covers, ruled with horizontal lines, and divided into four vertical columns. To measure proceed as follows:—Mark a number with the scribe on the butt end of the tree, and enter a similar number in the first column of the book; this will not only serve to identify the particular log, but prevent any risk of measuring twice. Should the taper throughout the whole length of the tree be tolerably gradual, set down the length in the second column of the book, opposite the number already entered. At exactly one-half of the length of the portion measured, take the girth by passing the girt-strap tightly around the stem. Put this down in the third column on the same horizontal line as the number and length. Should, however, the trunk taper not be fairly uniform throughout the entire length, as frequently happens, several measurements may require to be taken.

For example, a tree may be 36 ft. in length, running with regular taper for perhaps 12 ft., after which it branches out, reducing the size of the remaining part very considerably for, say another 12 ft., where it again branches and leaves the last 12 ft. of a relatively small size. With such a tree it would be quite impossible to obtain anything like a correct measurement by taking only one length and girth. The difficulty is, however, readily got over by first measuring the lower 12 ft., then the second, and then the third, marking the respective lengths and girths in the vertical columns as already described.

The measurement of these trees, so far as the field work is concerned, is now completed, the contents of each tree being found by referring to “Hoppus’s Measurer”—a book with which every forester should be supplied. By squaring the quarter-girth in inches, multiplying by the length in feet, and dividing by 144, the same result will be obtained. This is, however, a tedious method, especially where large numbers of trees have to be dealt with, and should only be adopted when Hoppus is not at hand.

By committing to memory the following short table of quarter-girths much time in calculating and consulting authorities will be saved.

6-inch quarter-girth will give contents equal to ¼ the entire length in feet. 7 ” ” ” ⅓ 8½ ” ” ” ½ 10 ” ” ” ⅔ 12 ” ” ” 1 13 ” ” ” 1¼ 14¾ ” ” ” 1½ 16 ” ” ” 1¾ 17 ” ” ” 2 19 ” ” ” 2½ 21 ” ” ” 3 22½ ” ” ” 3½ 24 ” ” ” 4 27 ” ” ” 5 29½ ” ” ” 6 31¾ ” ” ” 7 34 ” ” ” 8 36 ” ” ” 9

The sliding rule is also useful for determining contents.

The proper allowance to be made for bark is half an inch for every foot of quarter-girth for oak and elm under 12 in. quarter-girth, and an inch for all beyond, but it is quite impossible to fix upon any one uniform scale that will meet even the majority of circumstances. Trees growing in exposed situations will frequently have bark almost double the thickness of those of a similar size in the woodland. My plan has been always to allow for the bark of each tree at the time of measurement.

=Measuring Standing Timber.=—For this a pliable pole 18 ft. long, marked in feet, and the girt-strap already referred to are the necessary equipment. In estimating the number of feet of timber upon a large area, it is not always necessary to measure each tree separately, particularly when the whole situation is composed of one species, and the individual trees are about the same age and size, as by multiplying the total number of trees by the average content of those selected and measured a very just calculation will be arrived at. Great care in their selection, and considerable judgment in taking the average will, however, be required.

[Illustration: MEASURING HEIGHT OF TREES]

When each tree is to be measured separately two assistants will be required, one to carry the 18-ft. pole, and the other the girting-strap. Sometimes, when the timber is of great height, jointed bamboos are used, and a light ladder brought into requisition.

In carrying out the work in this way, the man with the pole declares the height of the tree, and the one with the tape the quarter-girth.

=Measuring the Height of Trees.=—There are several methods of ascertaining the heights of trees, but the two following are, perhaps, the most simple, and the appliances necessary quite inexpensive:—

No 1.—Take three laths, such as bricklayers use for tiling, and nail them in the shape of the frame shown; _a a_ must be of equal length; _a_ and _b_ being placed on the ground, the eye must follow up the larger lath _d d_ until it is in a line with _e_, the top of the tree or object you wish to measure.

The frame must be placed as level with the bottom of the tree as possible. Should the ground be very uneven you must give and take accordingly.

It will be seen that _b_ to _c_ is the same length as _c_ to _e_, and this gives the height of the tree.

No 2.—Suspend the triangle between the thumb and forefinger of the left hand, knuckles down, upon the point _a a_, allowing it to swing freely. The edge _b c_ will then fall perpendicularly, and _c d_ will be horizontal. The remaining edge _d b_ will then lie at an angle of 45 to the horizon. On this edge are two sights, _e_ and _f_. Look through _e_ until _f_ is aligned with the tree-top, advancing or retiring till the sights point exactly to it.

Then, if the observer’s feet are level with the tree root, the height of the tree is the distance from his feet to the root, plus the height of the eye from the ground.

The dendrometer is perhaps the most useful instrument for taking the height of a tree and can be procured from some of our nurserymen.