Admitting that experience, (which is the result either of observation or experiment,) is the only source of our knowledge of nature, still, before we can rightly interpret its phenomena, we must rid the mind of those prejudices which, like a false or uneven mirror, are apt to distort the truth. The mind of man,' says Bacon, is far from the nature of a clear and equal glass, wherein the beams of things should reflect according to their true incidence; nay, it is rather like an enchanted glass, full of superstition and imposture, if it be not delivered or reduced.'* Before the time of Bacon, no attempt had been made to detect and enumerate these prejudices or biases of the mind; and it was left for the great restorer of true philosophy to undertake so useful a task. This he accomplished in the first book of the Novum Organum, giving to these prejudices the significant name of idols of the under

*Bacon's Works, vol. 2, p. 190.

standing: because, like false divinities, they have withdrawn men from the worship of Truth.

These prejudices or idols are divided by Bacon into four classes, which he denominates Idola Tribus; Idola Specus; Idola Fori; and Idola Theatri: i. e., Idols of the Tribe, the Den, the Forum, and the Theatre.

1. The Idols of the Tribe are those prejudices which are inherent in human nature. Among these may be reckoned that disposition among men to assume the existence of a greater degree of order and uniformity in nature than experience is, in fact, found to justify; and thus when any thing inconsistent with this notion presents itself, it is either tortured, as it were, into reconcilement, or explained away. Thus, for example, as soon as the French geologists (MM. Cuvier and Brongniart) had accurately examined and described the tertiary strata of the Paris basin, an attempt was made to trace the

different subdivisions of this interesting group throughout Europe; and no sooner was a new tertiary formation discovered, as that of Italy, for instance, than geologists endeavoured to identify it with the Parisian type: every fancied feature of correspondence was dwelt upon and exaggerated into a likeness, whilst the wide difference in mineral character and organic contents was slurred over as trifling and unimportant. By the influence of this illusion,' says Mr. Lyell, the succession and chronological relations of different tertiary groups were kept out of sight;' and thus the progress of geology was greatly retarded.

• Principles of Geology, vol. 3, p. 17, (1833.) In referring to this valuable work, (which has done more to popularise the science of geology in this country, and to diffuse correct notions concerning it, than any publication which can be mentioned,) we cannot avoid observing, that it affords an excellent example of a most successful application of the Baconian or inductive method of research, to a department of science, of all others the most infested with idols and visionary hypotheses.

This illustration, drawn from a deservedly popular science, (and others from this and widely different branches of philosophy might easily be adduced,) shows that Bacon was justly warranted in expecting (as he did*) that although the idols of the mind might be thrown down, still, when philsophy had been re-edified, they would be again set up and worshipped.

2. The Idols of the Den are those that originate from the peculiar character of the man. Although our persons,' says Bacon,

live in the view of heaven, yet our spirits are included in the caves of our own complexions and customs, which minister unto us infinite errors and vain opinions, if they be not recalled to examination.'

Among the prejudices of this class none

* Novum Organum, Lib. 1, aph. 38. It is remarkable that so acute an observer as Dr. Copleston, the learned Bishop of Llandaff, should have asserted that 'there is not one of the Idola which is now defended or cherished in any seat of learning, or by any person of liberal education.'-Second Reply, p. 22.

deserve to be more strictly guarded against than those which spring from the particular studies to which one may be addicted. Habituated to a certain range of reading and reflection, a man's thoughts are apt to become, as it were, localised; and, as fabled of the cameleon, take their colour from surrounding objects. Aristotle, devoted to the study of metaphysics, carried his favourite pursuit, with all its verbal magic, into his physics; and thus corrupted that science, rendering it an almost everlasting source of controversy.

Dr. Gilbert, of Colchester, an inquirer to whose patient observations the modern science of electricity is much indebted,-is another example*. Having assiduously studied the subject of magnetism, with considerable success, he forthwith began to construct a system of philosophy, founded on his favourite pursuit.

* His Treatise on the Magnet' was published in 1590, and re-published at Ferrara in 1629, with a commentary by Cabæus, a learned Jesuit.