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.

eyes of them that look on; so such men's industries are in the eyes of others, or at least in regard of their own designments: only learned men love business, as an action according to nature, as agreeable to health find, as exercise is to health of body, ag pleasure in the action itself, and not the purchase; so that of all men they The most indefatigable, if it be towards suess which can hold or detain their

dha learning should take up too or leisure; I answer,' says Bacon,

dase active or busy man that hath been tach, no question, many vacant atures while he expecteth the tides business, (except he be either dispatch, or lightly and bitious to meddle in things er done by others :) and is but how those spaces eisure shall be filled and

a pleasures or in studies;

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.