primarily denotes a little stone or pebble, anciently used in making computations, taking of suffrages, playing at tables, and the like. In aftertimes, pieces of ivory, and counters struck of silver, gold, and other matters, were used in lieu thereof, but still retaining the ancient names. Computists were by the lawyers called calculators, when they were either slaves or newly freed men; those of a better condition were named calculatores or numerarii; ordinarily there was one of these in each family of distinction. The Roman judges anciently gave their opinions by calculi, which were white for absolution, and black for condemnation. Hence calculatus albus, in ancient writers, denotes a favourable vote, either in a person to be absolved and acquitted of a charge, or elected to some dignity or post; as calculatus niger did the contrary. This usage is said to have been borrowed from the Thracians, who marked their happy or prosperous days by white, and their unhappy by black, pebbles, put each night into an urn.

Besides the diversity of colour, there were some calculi also which had figures or characters engraven on them, as those which were in use in taking the suffrages both in the senate and at assemblies of the people. These calculi were made of thin wood, polished, and covered over with wax. Their form is still seen in some medals of the Cassian family; and the manner of casting them into the urns, in the medals of the Licinian family. The letters marked upon these calculi were U. R. for uti regat, and A for antiquo; the first of which expressed an approbation of the law, the latter a rejection of it. Afterwards the judges who sat in capital causes used calculi marked with the letter A for absolvus; C for condemnatus; and N. L. for non liquet, signifying that a more full information was required.

Calculus Humanus, the stone in the bladder or kidneys. These are commonly formed of different strata or incrustations; sometimes smooth and heavy like mineral stones; but oftener rough, spongy, light, and full of inequalities or protuberances: chemically analysed, or distilled in an open fire, they nearly yield the same principles as urine itself, or at least an empyreumatic volatile urinous matter, together with a great deal of air. They never have, nor can have, naturally, any foreign matter for a basis; but they may by accident; an instance of which is related by Dr. Percival. A bougie had unfortunately slipped into the bladder, and upon it a stone of considerable size was formed in less than a year. This stone had so much the appearance of chalk, that the Doctor was induced to try whether it could be converted into quicklime. His experiment succeeded, both with that and some other calculi; from which he conjectures, that hard waters which contain calcareous earth may contribute towards the formation of these calculi. See (the Index subjoined to) Medicine.

Calculus Specialis, or Literalis, is the same with Algebra.