admitted without examination.

Familiar ac

quaintance, it has been truly said, is perpetually mistaken for accurate knowledge;* and thus it is, that a patient attention to subjects that are known is as often needed as information on those of which we are ignorant. The history of science affords innumerable illustrations of the truth of this position. The vibrations of a lamp, suspended from the roof of the cathedral of Pisa, appearing to recur at equal intervals, arrested the attention of Galileo; who, having brought his observation to the test, by comparing the vibrations with the beat of his pulse, struck out the happy idea, that an instrument might be constructed which could be usefully employed by medical men (he was himself then studying medicine,) to ascertain, with a precision not then attainable, the rate of the

* Abp. Whately's Political Economy, Lect. IX., and Logic, p. 332. Dr. Copleston has made the same remark in the Preface to his 'Four Discourses,' xiii. See also Bacon's Works, vol. 2, p. 189.

human pulse and its variations from day to day. This led to the use of the pendulum as a measure of time. The lamp and its oscillations had been seen by thousands, and forgotten; but the youthful philosopher witnessed the phenomenon with thoughtful attention; and from a fact, apparently trivial, elicited one of the most valuable principles in science.

The history of the Voltaic pile affords another illustration, quite as striking as the last, of the importance in physical science, of not neglecting any phenomenon, however well known or apparently insignificant, for which we cannot account. The convulsive motion of a dead frog placed near an electrical machine, was a phenomenon which had long been known; but, until the time of Galvani, it had excited little or no philosophic inquiry. In 1790 that eminent anatomist turned his attention to the subject. His observations excited the curiosity of Volta, who, taking up the inquiry with great

ardour, succeeded in constructing one of the most wonderful instruments invented by man--the Voltaic pile: an instrument which, in the hands of our illustrious countryman Sir H. Davy, effected a total revolution in chemical science.

Having suggested various grounds of hope that, notwithstanding the prejudices and errors of past times, knowledge would, in future, stretch forth her branches to the seas and to the floods,' lord Bacon concludes the first book of his Novum Organum with the animating reflection, that if to extend the power of our country over mankind,—an empire only to be gained by wrongs and human sufferings,-be an object of eager pursuit, how much nobler is that ambition, --if ambition it can be called,-which seeks to obtain, by the pleasant and peaceful paths of science, dominion over Nature herself.*

*Novum Organum, lib. 1, aph. 129.

In the second book of the Novum Organum, lord Bacon proceeds to develop more fully his inductive method, and to exemplify it; selecting for this purpose the subject of Heat. From what has been already said, it is obvious that, in every subect of inquiry, the first step is to collect such facts or phenomena as in any way relate to it, not only those which spontaneously offer themselves, but such as can be elicited by experiment.

In this preliminary procedure, more skill and judgment are required than those unused to scientific pursuits will be prepared to expect.

It often happens that an object is not seen, from not knowing how to see it, rather than from any defect in the organ of vision. Mr. Babbage has given a striking illustration of this fact. Conversing with sir John Herschel on the dark lines observed in the solar spectrum by Fraunhofer, he inquired whether Mr. Babbage had seen

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them; and on his replying in the negative, sir John Herschel mentioned the extreme difficulty he had had, even with Fraunhofer's description in his hand, and the long time which it had cost him in detecting them: he then added, 'I will prepare the apparatus, and put you in such a position that they shall be visible, and yet you shall look for them and not find them: after which, while you remain in the same position, I will instruct you how to see them, and you shall see them, and not merely wonder you did not see them before, but you shall find it impossible to look at the spectrum without seeing them.' On looking as he was directed, notwithstanding the previous warning, Mr. Babbage did not see them; and, after some time, he inquired how they might be seen, when the prediction of sir John Herschel was completely fulfilled.* But if it be some

* Babbage's Reflections on the Decline of Science in England, pp. 210, 211.