In the exploitation of forests it is an important matter to be able to
measure the cubature of trees, and the process most generally employed
consists in determining their height and mean circumference, the
apparatus used for this latter measurement being compasses having the
form of the calipers used by mechanics. The figure indicated is read
upon the graduated rule and is called off in a loud voice to another
person, who at once writes it down. There are several causes of error:
it is possible that the reading may be incorrectly made or improperly
called off, or be misunderstood or incorrectly noted. Finally, it is a
somewhat fatiguing operation that is often dispensed with and the
measurement made by estimate. In order to do away with all such causes
of error, M. Jobez, a mining engineer, has had M. Peccaud construct
an apparatus that automatically registers all the measurements upon a
paper tape analogous to that used in the Morse telegraphic apparatus.
[Illustration: FIG. 1.--APPARATUS FOR OBTAINING THE CUBATURE OF
TREES.]
The registering mechanism (Fig. 1) is fixed to the movable branch that
forms the slide of the instrument. It is so arranged that when this
branch is slid along the rule carrying the graduations, a gearing
causes the revolution of a wheel, D, which carries figures
corresponding to such graduation. At the same time, two feed rollers,
E, cause a small portion of the paper tape (which is wound upon a
spool, A) to move forward and wind around a receiving spool, B. After
the apparatus has been made accurately 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 is taken of points; but this is of no importance,
since the error that might be made in misplacing one would be so great
that it would be immediately detected. A 2 franc tree would not be
confounded with a 20 or a 200 franc one. As an approximation, the
first two figures of the result are obtained accurately; and that
suffices, because, since the whole is based upon an approximate
measurement, which is the mean circumference of the tree, we cannot
exact absolute precision in the results. The essential thing is to
have a practically acceptable figure.--La Nature.
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EGYPT'S POPULATION, according to the census taken last June, is
9,750,000, more than double the population in 1846. The foreign
residents are 112,000; of these, 38,000 are Greeks, 24,500 Italians,
19,500 Britishers, including the army of occupation, and 14,000 French
subjects, including Algerians and Tunisians. Twelve per cent. of the
native males can read and write; the other Egyptians are illiterate.
Cairo has 570,000 inhabitants, Alexandria 320,000, Port Said 42,000,
and Suez 17,000.
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