.

Specific Specific Factors to be multiplied
Gravities. Floating Powers. into burden to find
weight of raft just
able to support it.
Alder........ .80 .25 4.0
Ash........... .85 .18 5.7
Beech......... .85 .18 5.7
Elm....... .59 to .80 .70 to .25 1.4 to 4.0
Fir...... .47 to .60 1.13 to .66 0.9 to 1.5
Larch..... ... .53 .89 1.1
Oak........... .75 .33 3.0
" heart of.. 1.17 sinks cannot be used
Pine..... .40 to .63 1.50 to .60 0.7 to 1.7
Poplar........ .38 1.63 0.6
Willow........ .59 .70 1.4

Examples: -- a raft of alder, weighing 200 lbs., would just support
200 x .25 or 50 lbs.
A burden of 100 lbs. would require a raft of alder, weighing not les
than 100 x 4.0, or 400 lbs. to support it.
Burning down Trees.--Where there are no means at hand to fell trees, they
should be burnt down; two men may attend to the burning of twenty trees
at one and the same time. When felled, their tops and branches, also, are
to be trimmed by fire. (See "Hutting Palisades.")

Reed Rafts.--Mr. Andersson, in exploring the Tioughe River, in South
Africa, met with two very simple forms of rafts: the one was a vast
quantity of reeds cut down, heaped into a stack of from 30 to 50 feet in
diameter, pushed out into the water, and allowed to float down stream:
each day, as the reeds became water-logged, more were cut and thrown on
the stack: its great bulk made it sure of passing over shallow places;
and when it struck against "snags," the force of the water soon slewed it
round and started it afresh. On an affair of this description, Mr.
Andersson, with seven attendants, and two canoes hauled up upon it,
descended the river for five days. The second reed raft was a small and
neat one, and used for ferries; it was a mattress of reeds, 5 feet long,
3 broad, and some 8 inches thick, tied together with strips of the reeds
themselves; to each of its four corners was fixed a post, made of an
upright faggot of reeds, 18 inches high; other faggots connected the tops
of the posts horizontally, in the place of rai