The _Abacus_ was variously contrived; that chiefly used in European countries was made by drawing any number of parallel lines at pleasure, at a distance from each other, equal to twice the diameter of a _calculus_ or counter. This placed on the lowest line, signified 1; on the second, 10; on the third, 100; on the fourth, 1000; on the fifth, 10,000; and so on. In the spaces between the lines, the same counters signified half of what they represented on the next superior line; viz. in the space between the first and second lines, 5; between the second and third, 50; between the third and fourth, 500; and so on. The abacus was also divided cross-wise into _areolæ_, and by this means subtractions were performed. The calculating instrument of Mr. Babbage is however much superior to any other contrivance yet suggested. No. LXXXV. A little ball, made in the shape of a plum or pear, which, being dexterously conveyed or forced into a body's mouth, shall presently shoot forth such, and so many bolts of each side and at both ends as, without the owner's key, can neither be opened nor filed off, being made of tempered steel, and as effectually locked as an iron chest. NOTE. The steel fangs with which this instrument is furnished must, like the bolt of a common latch, be chamfered from the point, so that, on its being inserted within the teeth, the bolts will instantaneously spring out; and no power short of the key previously made to fit the wards of the lock will suffice to free those who are thus ensnared. This is evidently one of those discoveries which, though practicable in itself, appears better calculated for swelling the catalogue of the noble Author's inventions, than for any beneficial result likely to accrue to the public from its discovery. No. LXXXVI. A chair made _à-la-mode_, and yet a stranger, being persuaded to sit down in it, shall have immediately his arms and thighs locked up, beyond his own power to loosen them. NOTE.