dew, which occasionally exhibit colour, and yet have nothing in common with the stones, flowers, and metals which possess colour permanently, except the colour itself. Hence Bacon concludes that colour is nothing else than a modification of the rays of light produced in the first case by the different degrees of incidence; and second by the texture or constitution of the surface of bodies. He may be considered as very fortunate in fixing on these examples, for it was by means of them that Newton afterwards found out the composition of light.

II. The instantia migrantes exhibit some property of the body passing from one condition to another, either from less to greater or from greater to less; arriving nearer perfection in the first case, or verging towards extinction in the second.

Suppose the thing inquired into were the cause of whiteness in bodies; an instantia migrans is found in glass, which entire is colourless, but pulverized becomes white. The same is the case with water unbroken or dashed into foam.

III. The instantiæ ostensive are the facts which show some particular property in its highest state of power and energy, when it is either freed from impediments which usually counteract it, or is itself of such force as entirely to repress those impediments.

If the weight of air were inquired into, the Torricellian experiment, or the barometer, affords an ostensive instance, where the circumstance which conceals the weight of the atmosphere in common cases, namely, the pressure of it in all directions, being entirely removed, that weight produces its

full effect, and sustains the whole column of mercury in the tube.

IV. The instances called analogous or parallel consist of facts between which a resemblance or analogy is visible in some particulars, notwithstanding great diversity in all the rest. Such are the telescope and microscope compared to the eye. It was the experiment of the camera obscura which led to the discovery of the formation of images of external objects in the bottom of the eye by the action of the crystalline lens, and other humours of which the eye is formed.

V. Instantiæ comitatus: examples of certain qualities which always accompany one another. Such are flame and heat-flame being always accompanied by heat, and the same degree of heat in a given substance being always accompanied with flame.

Hostile instances, or those of perpetual separation, are the reverse of the former. Thus transparency and malleability in solids are never combined.

VI. The instantia crucis. When in any investigation the understanding is placed in equilibrio, as it were, between two or more causes, each of which accounts equally well for the appearances, as far as they are known, nothing remains to be done, but to look out for a fact which can be explained by one of these causes and not by the other. Such facts perform the office of a cross, erected at the separation of two roads, to direct the traveller which to take: hence called crucial instances.

The experimentum crucis is of such weight in

matters of induction, that in all those branches of science where it cannot be resorted to (the circumstance of an experiment being out of our power and incapable of being varied at pleasure) there is often a great want of conclusive evidence. Such are the leading points of Bacon's analysis of the Inductive Method.

CHAPTER IV.

THE SPIRIT OF BACON'S WORKS.

FROM the foregoing exposition it will be seen that Bacon's method was not a vague formula, but a system of specific rules. He did not content himself with telling men to make observations and experiments: he told them how observations and experiments ought to be made. He did not content. himself with stating the proper method of investigation to be that of induction founded upon facts: he distinguished proper from improper inductionsthe "interrogation" from the "anticipation" of Nature.

His method may

He did this, and he did more. be said to have two parts: the one, that precise system of rules just spoken of; the other, that wise and pre-eminently scientific spirit which breathes through his works. This latter has given us those wise and weighty aphorisms which form perpetual texts for philosophical writers. It is this, more than his rules, which reveals to us the magnificence and profundity of his views. It is this which shows. us how completely he saw through the false methods of his day, and how justly he is entitled the father of positive science.

These aphorisms form, as we have said, perpetual texts. They are quoted on all occasions in which method is treated of by scientific men, We

cannot, however, resist quoting a half-dozen of them here, because of their exceeding value, and of their fitness as illustrations of his greatness :

I. Man, the minister and interpreter of Nature, can act and understand in as far as he has, either in fact or in thought, observed the order of Nature; more he can neither know nor do.

II. The real cause and root of almost all the evils in science is this: that, falsely magnifying and extolling the powers of the mind, we seek not its real helps.

III. There are two ways of searching after and discovering truth: the one, from sense and particulars, rises directly to the most general axioms, and resting upon these principles, and their unshaken truth, finds out intermediate axioms, and this is the method in use; but the other raises axioms from sense and particulars by a continued and gradual ascent, till at last it arrives at the most general axioms, which is the true way, but hitherto untried.

IV. The understanding, when left to itself, takes the first of these ways, for the mind delights in springing up to the most general axioms, that it may find rest; but after a short stay there, it disdains experience, and these mischiefs are at length increased by logic for the ostentation of disputes.

V. The natural human reasoning we, for the sake of clearness, call the anticipation of nature, as being a rash and hasty thing; and the reason duly exercised upon objects, we call the interpretation of nature.

VI. It is false to assert that human sense is the measure of things, since all perceptions, both of sense and mind, are with relation to man, and not