The flying railway.
Other vessels, not so well provided with spars as to entitle them to share in the accommodation of these stages, adopted a kind of flying railway, such as is used on the rocky coast of the Cape Verdes for the shipment of salt. A stout spar, 40ft. or 50ft. long, or sometimes, if the vessel was totally unprovided, her own mainboom was taken ashore. Smaller spars were set up as shears, and by these the large one was erected, and stayed in a perpendicular position as a derrick. The heaviest bower anchor, with several fathoms of chain, was laid outside the surf, in thirty or forty fathoms of water. A stout hawser was bent on to the end of the chain, carried to the derrick head, and hitched round it or otherwise secured; and the shore end was extended inland toward another anchor, to which it was hauled taut by a powerful tackle. Another tackle served to raise the guano bags to the derrick head, and on the hawser travelled a large snatch or natch block (so called because one of its sides is notched to admit any part of a line, the end of which cannot conveniently be reeved through). A man, seated on a kind of cross-tree, would pass the hook of the travelling block into the slings of the bags when they were hoisted, and would detach the hook of the tackle, and the bags were eased down to the boat lying out, where the hawser nearly reached the sea by a stout line passing through a single block at the derrick head. Generally, the travelling block alone had to be brought back; but if provisions or other stores were to be landed, they were hooked on before it returned. Passengers would be landed or embarked in the same manner; sometimes in a stout basket, or in a cask cut into the fashion of an arm-chair; but more generally, in disdain of such luxuries, in the loops of a double bowline—the bolder spirits glorying in being let go by the run, and gliding down the hawser just as the Russians do in their sledges on artificial ice hills.
It will often happen that in the erection of some makeshift contrivance, or the laying out of a ground plan for future operations, some rough and ready mode of levelling will be needed.
Levelling.
The Dutch African farmers use a very simple and effective level in laying out water furrows for the irrigation of their farms, and, when it is understood that even on very favourable ground these furrows are often two miles long, it will be seen that some little engineering is required. They take a table, the longer the better, and having tested its surface by the eye, and by lines stretched across, they place on each end a large basin filled to the brim with water. When these are perfectly full without overflowing, the sight is taken over them at a staff set up upon the next station, and the height of the mark on this, less the height of the table and basin, gives the difference of level.
SOUTH-AFRICAN LEVELLING TABLE.
We had a tube of tin 4ft. long and 1in. diameter, with two pieces of glass tube bent upward, passing through corks in either end, so that, by using water coloured with charcoal or mud, we could at once observe the true level. A long bamboo or reed closed at the ends, but open in all its intermediate length, will do just as well, and there is no necessity that it should be straight. Smaller pieces of reed, 3in. or 4in. long, should be set up in each end, and the bore of these must be large enough to allow the water to flow freely to its natural level. The top of these may be notched for sights like those of a rifle, or sliding sights may be fitted on the side of them. This instrument may be used for taking vertical angles by fixing the eyesight upon a pivot, marking the place of the foresight on the staff, when the level has been taken; then pouring away the water, sighting the top of the object, marking the elevation upon the staff, and then either drawing the obtained angle on paper, or taking the difference between the base and perpendicular, and then working out the result by the rule of three.
Deodar bridges.
