Part 8 (1/2)
Makes.h.i.+ft Life-belt.--A moderately effective life-belt may be made of holland, ticking, canvas, or similar materials, in the following manner, and might be used with advantage by the crew of a vessel aground some way from the mainland, who are about to swim for their lives:--Cut out two complete rings, of 16 inches outer diameter and 8 inches inner diameter; sew these together along both edges, with as fine a needle as possible and with double thread: add strong shoulder-straps, so that it shall not, by any possibility, slip down over the hips; and, lastly, sew into it a long narrow tube, made out of a strip, a foot long and two inches wide, of the same material as the belt. At the mouth of this, a bit of wood, an inch long, with a hole bored down its middle, should be inserted as a mouthpiece. Through this tube the belt can be re-inflated by the swimmer while in the water, as often as may be necessary; and, by simply twisting the tube and tucking its end in the belt, its vent can always be closed.
After a canvas belt is thoroughly drenched, it will hold the air very fairly: the seams are its weakest parts. For supporting a swimmer in calm water, a collar is as good as a belt.
Transport on Water.--Parcels.--The swimmer's valuables may as well be put inside the empty vessel that acts as his float, as in the turban on his head (see ”Floats”). A goat-skin is often filled half full of the things he wants to carry, and is then blown out and its mouth secured. A very good life-belt may be bought, which admits of this arrangement: it has a large opening at one end, which is closed by a bra.s.s door that shuts like the top of an inkstand, and is then quite air-tight.
A small parcel, if tightly wrapped up in many folds, will keep dry for a long time, though partly immersed in water: the outside of it may be greased, oiled, or waxed, for additional security. If deeply immersed, the water is sure to get in.
Swimming with Horses.--In crossing a deep river, with a horse or other large animal, drive him in: or even lead him along a steep bank, and push him sideways, suddenly into the water: having fairly started him, jump in yourself, seize his tail, and let him tow you across. If he turns his head with the intention of changing his course, splash water in his face with your right or left hand, as the case may be, holding the tail with one hand and splas.h.i.+ng with the other; and you will, in this way, direct him just as you like. This is by far the best way of swimming a horse: all others are objectionable and even dangerous with animals new to the work,--such as to swim alongside the horse, with one hand on his shoulder; or, worst of all, to retain your seat on his back. If this last method be persisted in, at least let the rider take his feet out of the stirrups, before entering the water.
[Sketch of horse and man crossing river].
To float a Wagon across a River.--It must be well ballasted, or it will a.s.suredly capsize: the heavy contents should be stowed at the bottom; the planking lashed to the axletrees, or it will float away from them; great bundles of reeds and the empty water-vessels should be made fast high above all, and then the wagon will cross without danger. When it is fairly under weigh, the oxen will swim it across, pulling in their yokes.
Water Spectacles.--When a man opens his eyes under water, he can see nothing distinctly; but everything is as much out of focus, as if he looked, in air, through a pair of powerful spectacles that were utterly unsuited to him. He cannot distinguish the letters of the largest print in a newspaper advertis.e.m.e.nt; he cannot see the s.p.a.ces between the outstretched fingers, at arm's length, in clear water; nor at a few inches' distance in water that is somewhat opaque. I read a short paper on this subject, at the British a.s.sociation in 1865, in which I showed the precise cause of this imperfection of vision and how it might be remedied. If the front of our eyeb.a.l.l.s had been flat, we should have had the power of seeing under water as clearly as in air; but instead of being flat, they are very convex, consequently our eye stamps a concave lens of high power into the water, and it is the seeing through this concave eyegla.s.s which our eyeball makes for itself, that causes the indistinctness of our vision. Knowing the curvature of the eyeball, it is easy to calculate (as I did in the memoir mentioned above) the curvature of a convex lens of flint-gla.s.s that should, when plunged into water, produce effects of an exactly equal and contrary value, exactly neutralizing the effects of the concave eyegla.s.s of water, if it were held immediately in front of the pupil of the eye. I have made several experiments with a view to obtaining serviceable spectacles, for seeing under water. The result is as follows:--experience has shown the distance from the eyeball at which spectacle-gla.s.ses can be most conveniently placed; now at that distance, the joint effect of the concave water-lens and the convex gla.s.s spectacle-lens, is to produce an opera-gla.s.s of exceedingly low magnifying power, that requires a small adjustment for accurate definition at different distances.
If the spectacle-lens be of flint-gla.s.s and doubly convex, each of its faces should have a curvature of not greater than 6 1/2 tenths of an inch, nor more than 8 1/2 tenths of an inch in radius: within these limits, it is practicable to obtain perfectly distinct vision under water by pressing the spectacles forwards or backwards to a moderate degree.
Lenses of these high magnifying powers are sometimes sold by spectacle-makers, for persons who have undergone an operation for cataract. I have tried, but hitherto without much success, to arrange the fittings by which the lenses are secured so that by a movement of the jaw or by an elevation of the eyebrows, I could give the necessary adjustment of the gla.s.ses, leaving my hands free for the purpose of swimming. (See also, under ”Fis.h.i.+ng;' 'To see Things deep under Water.')
RAFTS AND BOATS.
Rafts.--Rafts of Wood.--Rafts are made of logs of wood, held together by pairs of cross-bars, one of each pair lying above the raft and the other below; then, the whole may be made quite firm by a little judicious notching wherethe logs cross, and a few pegs and las.h.i.+ngs. Briers, woodbines, etc., will do for these. If the logs are large, they should be separately launched into the river, and towed into their proper places.
Outriggers vastly increase the stability of a raft. The raft-fastening in common use is shown in f. 1: it is a stout, little wand, bent over the cross piece, and wedged into holes in the framework.
[Sketch of raft].
[Fig 1 and Fig 2 show fastening arrangements].
The rafts of European rivers are usually built on sh.o.r.e, and launched into the water: three slides are laid for the purpose, on the sloping bank of the river; upon these are laid the four poles, secured together by their ends, which are to form the framework of the raft (fig. 2).
Other poles are put in between, until the whole is complete.
Bamboo rafts.--Where bamboo is plentiful, it is preferable to any other material for rafts. A few bamboos lashed into the shape of an ordinary field gate, but with two diagonals, and with handfuls of gra.s.s thrown on to make a platform, is very buoyant and serviceable.
Floating power of various Woods.--The floating power of a raft depends on the buoyancy of the wood of which it is made. I give, in a Table (p. 90), a list of the specific gravities of a few well-known woods; and have annexed to them a column of what may be called their ”specific floating powers.”*
[Footnote] *Specific floating power = (1/Spec. Gr.)--1. (Mem., the Table of these, in previous editions is incorrect.) Burden = weight of raft x specific floating power. Weight of wood required to support a given burden = Burden x (Spec. Gr./1-Spec. Gr.); the last column gives the latter factor.
Hence, to find the actual floating power of a raft, it is simply necessary to multiply its weight into the specific floating power of the wood of which it is made.
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 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.”)