But if the cause be, like the sun-spots, not under control, the inquirer will watch on all sides what events follow their appearance and development; he must watch for consequences of the new cause he is studying in many different circumstances, that his observations may satisfy the canons of proof.  But he will also resort for guidance to deduction; arguing from the nature of the cause, if anything is known of its nature, what consequences may be expected, and comparing the results of this deduction with any consequent which he suspects to be connected with the cause.  And if the results of deduction and observation agree, he will still consider whether the facts observed may not be due to some other cause.

A cause, however, may be under control and yet be too dangerous to experiment with; such as the effects of a poison—­though, if too dangerous to experiment with upon man, it may be tried upon animals; or such as a proposed change of the constitution by legislation; or even some minor Act of Parliament, for altering the Poor Law, or regulating the hours of labour.  Here the first step must be deductive.  We must ask what consequences are to be expected from the nature of the change (comparing it with similar changes), and from the laws of the special circumstances in which it is to operate?  And sometimes we may partially verify our deduction by trying experiments upon a small scale or in a mild form.  There are conflicting deductions as to the probable effect of giving Home Rule to Ireland; and experiments have been made in more or less similar cases, as in the Colonies and in some foreign countries.  As to the proposal to make eight hours the legal limit of a day’s labour in all trades, we have all tried to forecast the consequences of this; and by way of verification we might begin with nine hours; or we might induce some other country to try the experiment first.  Still, no verification by experiments on a small scale, or in a mild form, or in somewhat similar yet different circumstances, can be considered logically conclusive.  What proofs are conclusive we shall see in the following chapters.

Sec. 2.  To begin with the conditions of direct Induction.—­An Induction is an universal real proposition, based on observation, in reliance on the uniformity of Nature:  when well ascertained, it is called a Law.  Thus, that all life depends on the presence of oxygen is (1) an universal proposition; (2) a real one, since the ‘presence of oxygen’ is not connoted by ‘life’; (3) it is based on observation; (4) it relies on the uniformity of Nature, since all cases of life have not been examined.

Such a proposition is here called ‘an induction,’ when it is inductively proved; that is, proved by facts, not merely deduced from more general premises (except the premise of Nature’s uniformity):  and by the ‘process of induction’ is meant the method of inductive proof.  The phrase ‘process of induction’ is often used in another sense, namely for the inference or judgment by which such propositions are arrived at.  But it is better to call this ‘the process of hypothesis,’ and to regard it as a preliminary to the process of induction (that is, proof), as furnishing the hypothesis which, if it can stand the proper tests, becomes an induction or law.