Bacon's method relied on experimental "histories" to eliminate alternative theories. Bacon explains how his method is applied in his "Novum Organum" (published 1620). In an example he gives on the examination of the nature of heat, Bacon creates two tables, the first of which he names "Table of Essence and Presence", enumerating the many various circumstances under which we find heat. In the other table, labelled "Table of Deviation, or of Absence in Proximity", he lists circumstances which bear resemblance to those of the first table except for the absence of heat. From an analysis of what he calls the "natures" (light emitting, heavy, colored, etc.) of the items in these lists we are brought to conclusions about the "form nature", or cause, of heat. Those natures which are always present in the first table, but never in the second are deemed to be the cause of heat.