The Baconian method is the investigative method developed by Francis Bacon. It is an early forerunner of the scientific method. The method was put forward in Bacon's book Novum Organum, or 'New Instrument', and was supposed to replace the methods put forward in Aristotle's Organon.
Bacon suggests that you draw up a list of all things in which the phenomenon you are trying to explain occurs, as well as a list of things in which it does not occur. Then you rank your lists according to the degree in which the phenomenon occurs in each one. Then you should be able to deduce what factors match the occurrence of the phenomenon in one list and don't occur in the other list, and also what factors change in accordance with the way the data had been ranked. From this Bacon concludes you should be able to deduce by elimination and inductive reasoning what is the cause underlying the phenomenon.
Thus, if an army is successful when commanded by Essex, and not successful when not commanded by Essex: and when it is more or less successful according to the degree of involvement of Essex as its commander, then it is scientifically reasonable to say that being commanded by Essex is causally related to the army's success.
Bacon also listed what he called the Idols of The Mind. He described these as things which obstructed the path of correct scientific reasoning.
The Baconian method was further developed and promoted by English philosopher John Stuart Mill. His 1843 book, A System of Logic, was an effort to shed further light on issues of causation. In this work, he formulated the five principles of inductive reasoning now known as Mill's methods.