9o
Art of Travel.
Thus, a raft of 12 logs of larch, averaging 30 lbs. each, weighs 360 lbs. ; this multiplied by •47, is equal to 169 lbs. very nearly, which is the weight the raft will support without
sinking. |
Poplar is the lightest on the list. |
||||
Specific Gracities. |
Specific Floating Powers, |
Factors to be multiplied into burden to find weight of raft just able to support it. | |||
Alder |
25 |
4'0 | |||
Ash |
„ „ |
85 |
13 |
5.7 | |
Beech |
.. „ |
85 |
18 |
5.7 | |
Elm |
to '80 |
'70 to '25 |
1.4 to 4.0 | ||
Fir |
to •60 |
1.13 to '66 |
0.9to1.5 | ||
Larch |
89 |
1.1 | |||
Oak |
75 1.17 |
'33 sinks |
3.0 cannot be used | ||
„ heart of | |||||
Pine |
40 to • 63 |
1.50 to •60 |
0' 7 to 1.7 | ||
Poplar |
38 |
l•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 less 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 Rifts.-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
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