created and kept alive in the mind: we see how much we have yet to acquire, and the desire of making the acquisition becomes more ardent and habitually ope rative; and by prompting us to aim at a higher and a more distant standard than that to which we would otherwise conform, we are able by a sure, though gradual advancement, to make attainments which at one period it might be deemed presumption in us to anticipate.

A wide survey of human knowledge is useful in this and in many other respects, after we restrict our attention to the study of one branch. It gives so much enlargement to the mind as sets it free from the influence of prejudices; and as prevents it especially from giving way to that fruitful source of error, to which professional men are peculiarly liable, of deducing important conclusions from slight and fanciful analogies. The proneness of men to judge of things of which they are perfectly ignorant, from the rules that are applicable to subjects with which they are familiar, has been one of the greatest obstacles to the progress of science; and its universal prevalence, embracing men of every order and of every profession, has rendered it a matter of common remark. To this disposition of human nature may be traced nearly all the hypothetical systems that from the remotest ages downwards have been substituted for knowledge; and it is to this copious source of error more especially that we ascribe the attempts of physiologists to materialize the affections of mind, and to maintain that there is nothing but matter in the universe. We smile at the ancient chemists who were accustomed to ex

plain all the mysteries of nature, and of religion, by salt, sulphur, and mercury; and at the musician, mentioned by Mr. Locke, who believed that God created the world in six days and rested the seventh, because there are seven notes in music; but there are mistakes committed every day in common life, of still greater consequence, arising from the same prejudice. Hence the aphorism, that all men judge of others by themselves. "The selfish man thinks all pretences to benevolence and public spirit to be mere hypocrisy or self-deceit. The generous and open-hearted believe fair pretences too easily, and are apt to think men better than they really are. The abandoned and profligate can hardly be persuaded that there is any such thing as real virtue in the world. The rustic forms his notions of the manners and characters of men from those of his country village, and is easily duped when he comes into a great city."

"When men of confined scientific pursuits," says Bacon, “afterwards betake themselves to philosophy, and to general contemplations, they are apt to wrest and corrupt them with their former conceits." The same remark has been made by all our most distinguished philosophers. "Let a man," says Locke, "be given up to the contemplation of one sort of knowledge, and that will become every thing. The mind will take such a tincture from a familiarity with that object, that every thing else, how remote soever, will be brought under the same view. A metaphysician will bring ploughing and gardening immediately to abstract notions; the history of nature will signify nothing to him. An alchemist, on the contrary, will reduce divinity to the

maxims of his laboratory, explain morality by sal, sulphur, and mercury, and allegorize the scripture itself into the philosopher's stone. It is of no small consequence to keep the mind from such a possession, which, I think, is best done by giving it a fair and equal view of the whole intellectual world, wherein it may see the order, rank, and beauty of the whole, and give a just allowance to the distinct provinces of the several sciences in the due order and usefulness of each of them." "The same reason," says Berkeley, "that bids me trust a skilful artist in his art, inclines me to suspect him out of his art. Men are too apt to reduce unknown things to the standard of what they know, and bring a prejudice or tincture from things they have been conversant in, to judge thereby of things in which they have not been conversant. have known a fiddler gravely teach that the soul was harmony; a geometrician very positive that the soul must be extended; and a physician, who having pickled half a dozen embryos, and dissected as many cats and frogs, grew conceited, and affirmed there was no soul at all, and that it was a vulgar error.'

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These observations might be confirmed by a reference to the history of science. Before the time of Newton, the greatest hindrances in natural philosophy arose from men applying to it their previous notions. They confounded and mingled the phenomena of nature with their metaphysical speculations. Des Cartes, being a great mathematician, endeavoured to reduce nature to geometry, and so considered nothing in body but extension. The celebrated Dr. Hooke, whose genius was so strongly inclined to mechanics, and to

whom the art of watchmaking had, from his earliest years, been a favourite study, applied his notions to the explanation of the phenomena of the human mind, and endeavoured to account for its operations on the principles of mechanics. There is a curious fragment of this sort of physiologico-metaphysical speculation quoted by Professor Stewart, in his Philosophical Essays, in which the author speaks of a continued chain of ideas coiled up in the repository of the brain, the first end of which is farthest removed from the centre, or seat of the soul, where the ideas are formed, and the other end is always at the centre, being the last idea formed, which is always the moment present when considered. Hartley and Darwin being, from their profession as physicians, familiar with some of the phenomena and laws of matter, when they began to speculate on the human mind, reduced its faculties and its phenomena into materialism. In truth, the number of individual cases is endless, which might be adduced in illustration of Lord Bacon's remark already quoted; "that when men of confined scientific pursuits. afterwards betake themselves to philosophy, and to general contemplations, they are apt to wrest and corrupt them with their former conceits."

"The propensity which all men have to explain the intellectual phenomena, by analogies borrowed from the material world, has its origin in an error, differing from that which misled Hooke and Darwin, only in this, that the latter, being the natural result of the favourite, or of the professional habits of the individual, assumes as many different shapes as the pursuits of mankind; whereas the former, having its root in the common

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principles and common circumstances of the human race, may be expected to exert its influence on the theories of philosophers, in every country and in every age. The one prejudice would have been classed by Bacon with the idola species; the other with the idola tribus."

Now, as in practice this narrow way of judging is only to be cured by an extensive intercourse with men of different ranks, and professions, and nations; so in speculation we cannot promise ourselves an exemption from innumerable prejudices and mistakes, but by taking an enlarged view of the different branches of human knowledge. For though our acquaintance with many of them must after all be extremely superficial, yet it is sufficiently extended to keep it in continual remembrance, that what holds true in one science may not at all be applicable to another; and that therefore we cannot be sure of the accuracy of the judgments which we form, on subjects that are beyond the line of our pursuits.

Though it is not my intention to point out all the advantages to be derived from a general knowledge of science, I cannot but notice the important benefit which it affords us in that particular study to which we give our chief attention, by presenting it in new relations and under new aspects. It is this which gives a power to the man of general acquirements to bring a richness and variety of original illustration to the discussion of his subject, and to place it in such different lights as to surround it, even after it has been hackneyed by others, with all the air of novelty and freshness. This talent is, no doubt, accompanied with boldness of conception, and vigour of understanding;