The essential character of all tabular aids to computation is, that the results of many operations are recorded in some systematic way for easy reference, and that thereby the computer is spared the toil of obtaining these results for himself.

In many cases this constitutes almost the whole advantage of the table. Thus when, instead of extracting the cube root of some number, we take it from a printed book, we are merely using another's labour. The gain to the calculating community is, that the oft-repeated extraction of the same root is avoided. We also gain by the facility of systematic calculation; the labour of computing a series of successive results being in general only a small fraction of that which would have attended the same work performed in a desultory manner.

It is natural to suppose that soon after it became known that injurious effects follow the introduction of certain substances into the system, attempts were made to remedy these effects, and also to discover counteragents, or antidotes, to the hurtful substances. The success attending these attempts must, of necessity, have been closely related to the existing state of knowledge regarding the actions of active substances. When the effects of poisons were referred to supernatural manifestations, it was chiefly charms and superstitious rites that were trusted to as protectives and remedies. At a somewhat more advanced period in the progress of human knowledge, vague notions of physiological laws and processes supplied the indications of curative treatment.