ly to embrace the trunk of the
tree to be measured, it is removed and a pressure given to the lever,
H, which applies the paper to the type wheel, D. A special button
permits, in addition, of making a dot alongside of the numbers, if it
be desired to attract attention to one of the measurements, either for
distinguishing one kind of a tree from another or for any other
reason.

With this apparatus one man can make all the measurements and inscribe
them without any possible error and without any fatigue. It is
possible for him to inscribe a thousand numbers an hour, and the tapes
are long enough to permit of 4,000 measurements being made without a
change of paper. There is, therefore, a saving of time as well as
perfect accuracy in the operation.

In order to make the calculations necessary for the estimate, M.
Laurand has devised a sliding rule which facilitates the operation and
which is based upon the method that consists in knowing the height and
mean circumference of the tree. The circumference taken in the middle
is divided by 4, 4.8 or 5 according as one employs the quarter without
deduction or the sixth or fifth deduced. This first result, multiplied
by itself and by the height, gives the cubature of the tree. As for
the value, that is the product of this latter number by the price per
cubic meter. It will be seen that there is a series of somewhat
lengthy operations to be performed, and it is in order to dispense
with these that has been constructed the rule under consideration,
which, like all calculating rules, consists of two parts, one of which
slides upon the other (Fig. 2). Upon each of these there are two
graduated scales, or four in all, the first of which is designed for
the circumference and the second for the height of the tree, the third
for the price of the cubic meter and the fourth for the total result,
that is, the value of the entire tree. The arrangements are such that,
after the number corresponding to the circumference of the tree has
been brought opposite that corresponding to its height, the result
will be found opposite the price per cubic meter.

[Illustration: FIG. 2.--LAURAND'S CALCULATING RULE.]

Thus, in the position represented in the figure, we may suppose a tree
having a circumference of 2.5 m. and a height of 3.2 m.; then, if a
cubic meter is worth 25 francs, the tree will be worth 20 francs.

In order to simplify the calculations and the construction of the
rule, no account