CAPTAIN KYNASTON, C.B., R.N., whose apparatus for lowering ships' boats was recently described in this Magazine, has subsequently invented and patented a slip or disengaging hook which possesses several important merits. It is well known that the use of a jointed hook has been found of advantage for many purposes, such as the disengagement of the lowering tackle from ships' boats, the loosing of weight from cranes, &c. The detachment of heavy purchase blocks themselves, which is a laborious, and sometimes a hazardous operation on board ship, might very usefully be effected by means of a properly-constructed jointed hook. But the principal hook of this description - Mr. Shore's - in which the disengagement is effected by the use of a counterbalance, is attended by the disadvantages that it will not release the object attached to it while a strain is exerted upon it (which is always the case when a boat is lowered from a ship under way for example), it is liable to accidental disengagement by jerks, &c.

Now the object of Captain Kynaston's invention is to provide a hook which may with ease and certainty be released from any body to which it is attached, or which is attached to it, whether the pressure or pull exerted upon the hook be great or small, uniform or variable; and the invention consists of a hook constructed as represented in Fig. 1 of the engravings on the preceding page. He mounts a hook, a, upon a pin or centre, a', which is supported by and between two curved plates or guard pieces, b, b, and by means of a second pin or centre, c, connects to the back of the hook, a, a link, d, which passes up between the plates or guard pieces, b, b, and receives at its end, e, the chain, rope, bolt, or other object, to which the hook itself is to be connected, and by which the strain put upon the hook, a, is to be borne. The two pins, or centres, a' and c, are so placed that when a strain is put upon the hook, a, it will turn about the pin or centre, c, in the link, d, until the loop or eye by which the strain is put upon the hook, a, is allowed to fall or slip freely from it. To prevent this occurring, except when it is desired to release the hook, a shifting pin or bolt, f, is passed through the plates or guard pieces, b, b, in front of the stem, b', of the hook, a, to form a stop to prevent the said hook from turning as described. The same end may be attained by placing pulleys or sheaves, g,g', in the ends of the hook stem and of the link, d, through which pulleys a line, h, may be rove and made fast either to the link, d, or elsewhere. By withdrawing the aforesaid pin or bolt, f, in the one case, and by loosening the line or cord, h, in the other, the hook, a, will be disengaged. The two arrangements may be sometimes combined advantageously in the same hook. The plates or guard pieces, b, b, are so formed that when the hook is supporting a strain, the point of the hook, a, lies between them; and the loop or eye, i, by which the strain, is put upon the hook, a, is thus effectually prevented from accidentally releasing itself.

At Fig. 2 we have shown a plan of applying Captain Kynaston's improved hook to relieving tackles for disengaging a boat. In this Fig. the hooks are inverted, and the boat it supposed to be hung as heavy boats are commonly hung in the navy. A, A, are belaying pins added to the hooks for enabling each hook to be secured independently when hoisting up a boat, a man to each rope or line, h, securing them as the boat is hooked on. When the boat is hoisted up, the shifting bolts, f, f (Fig. 1), are inserted through the guide plates, b, b; the tackle, ropes, or lines, h, are thus relieved of strain, and are taken of the belaying pins, A, A. The ropes, h, are connected as shown in the Fig., and the end, B, being hauled taut and secured in any convenient part of the boat, the shifting bolts, f, f, are taken out, when the boat will be ready for lowering. On letting go the rope, B, both hooks will be opened, and the boat will be immediately disengaged.

It will be manifest to our nautical readers that changes involved in the use of the improved hook are of the simplest kind, and of the utility of such a hook they cannot have a doubt. It may not be amiss to mention a case in which it would have been invaluable. On the coast of the Bay of Biscay a short time since a brig was driven ashore, in presence of a man-of-war steamer. The commanding officer of the latter ordered a junior officer to have a boat lowered, and take certain measures for the brig's assistance. The wind and sea were very high at the time, and the officer despatched assured us that his men expended fifteen minutes in endevouring to unhook the lowering tackle from the boat.

We must not omit to mention that Captain Kynaston's hook will be found invaluable far releasing towing cables.