A way to lock all the boxes of a cabinet (though never so many) at one time, which were, by particular keys appropriated to each lock, opened severally, and independent the one of the other, as much as concerneth the opening of them, and by these means cannot be left open unawares. NOTE. This suggestion, which is both ingenious and useful, might be advantageously adopted in every description of cabinet or chest now in use; it may be performed either by cranks and wires, or by sliding bolts and levers communicating with each lock: the latter way, though attended with greater expense, is by far the most durable. Another and more simple mode offers itself in the use of a series of spring locks, which may be closed by the pressure of the lid, unconnected with any other mechanism. No. LXXX. How to make a pistol barrel no thicker than a shilling, and yet able to endure a musket proof of powder and bullet. NOTE. It requires no great share of ingenuity to accomplish this object, as an examination of modern fire-arms will fully testify; many pocket pistols that are manufactured at the present period, being at least as thin as those described by the noble author. No. LXXXI. A comb-conveyance carrying of letters without suspicion, the head being opened with a needle screw, drawing a spring towards one; the comb being made but after an usual form, carried in one's pocket. NOTE. A pocket comb and portable spoon, as described in this and the following article, with double sides to conceal any letter, paper, &c. are too simple to need a particular description. No. LXXXII. A knife, spoon, or fork, in an usual portable case, may have the like conveyances in their handles. No. LXXXIII. A rasping-mill for hartshorn, whereby a child may do the work of half-a-dozen men, commonly taken up with that work. NOTE. A variety of engines have been invented for this purpose, many of which are capable of effecting the saving of labour described by the Marquis, as at that period (1663) the process was usually effected by rubbing the horn or ivory over a common iron grater. No. LXXXIV. An instrument whereby persons, ignorant in arithmetic, may perfectly observe numeration and subtraction of all sums and fractions. NOTE. Sir Samuel Morland has published a detailed account of two instruments of this kind in a tract entitled, _The Description and Use of two Arithmetic Instruments_, &c.--London, 1673. The Roman _Abacus_ and Chinese _Swan-pan_ are also instruments of a like description.