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(4). Page 509. Mr. Airy's explanation of the phenomena termed by Sir D. Brewster a new property of light, is completed in the Philosophical Magazine for Nov. 1846. It is there shown that a dependence of the breadth of the bands upon the aperture of the pupil, which had been supposed to result from the theory, and which does not appear in the experiment, did really result from certain limited conditions of the hypothesis, which conditions do not belong to the experiment; and that when the problem is solved without those limitations, the discrepance of theory and observation vanishes: so that, as Mr. Airy says, “this very remarkable experiment, which long appeared inexplicable, seems destined to give one of the strongest confirmations to the Undulatory Theory.”

TRINITY COLLEGE, CAMBRIDGE,

November 7, 1846.

PREFACE TO THE FIRST EDITION.

At the present day, any endeavour to improve and extend the Philosophy of Science may hope to excite some interest. All persons of cultivated minds will agree, that a very important advantage would be gained, if any light could be thrown upon the modes of discovering truth, the powers that we possess for this end, and the points to which these may most profitably be applied. Most men, too, will allow, that in these respects much remains to be done. The attempts of this kind, made from time to time, are far from rendering future efforts superfluous. For example, the Great Reform of Philosophy and Method, in which Bacon so eloquently called upon men to unite their exertions in his day, has, even in ours, been very imperfectly carried into effect. And, even if his plan had been fully executed, it would now require to be pursued and extended. If Bacon had weighed well all that Science had achieved in his time, and had laid down a complete scheme of rules for scientific research, so far as they could be collected from the lights of that age, it would still be incumbent upon the philosophical world to augment as well as preserve the inheritance which he left; by combining with his doctrines such new views as the advances of later times cannot fail to produce or suggest; and by endeavouring to provide, for every kind of truth, methods of research as effective VOL. I.

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as those to which we owe the clearest and surest portions of our knowledge. Such a renovation and extension of the reform of philosophy appears to belong peculiarly to our own time. We may discern no few or doubtful presages of its approach; and an attempt to give form and connexion to the elements of such a scheme cannot now be considered premature.

The Novum Organon of Bacon was suitably ushered into the world by his Advancement of Learning; and any attempt to continue and extend his Reform of the Methods and Philosophy of Science may, like his, be most fitly preceded by, and founded upon, a comprehensive Survey of the existing state of human knowledge. The wish to contribute something, however little it may be, to such a Reform, gave rise to that study of the History of Science of which the present Work is the fruit. And the effect of these researches has been, a persuasion, that we need not despair of seeing, even in our own time, a renovation of sound philosophy, directed by the light which the History of Science sheds. reform, when its Epoch shall arrive, will not be the work of any single writer, but the result of the intellectual tendencies of the age. He who is most forward in the work will wisely repeat the confession of his sagacious predecessor : Ipse certè (ut ingenue fatear) soleo æstimare hoc opus magis pro partu Temporis quàm Ingenii.

To such a work, whensoever and by whomsoever executed, I venture to hope that the present Volumes may be usefully subservient. But I trust, also, that

Such a

in its independent character, as a History, this book may be found not altogether unworthy of the aim which its title implies.

It is impossible not to see that the writer of such a history imposes upon himself a task of no ordinary difficulty and delicacy; since it is necessary for him to pronounce a judgment upon the characters and achievements of all the great physical philosophers of all

ages, and in all sciences. But the assumption of this judicial position is so inevitably involved in the functions of the historian (whatever be his subject), that he cannot justly be deemed presumptuous on that account. It is true, that the historian of the progress of science is required by his undertaking to judge of the merits of men, in reference to subjects which demand a far intenser and more methodical study than the historian of practical life gives to the actions of which he treats; and the general voice of mankind,—which may often serve as a guide, because it rarely errs widely or permanently in its estimate of those who are prominent in public life,—is of little value when it speaks of things belonging to the region of exact science. But to balance these disadvantages, and to enable us to judge of the characters who must figure in our history, we may recollect that we have before us, not the record only of their actions, but the actions themselves; for the acts of a philosopher are his writings. We do not receive his exploits on tradition, but by sight; we do not read of him, we read him. And if I may speak of my own grounds of trust and encouragement in venturing on such a task, I knew that my life had been principally spent in those studies which were most requisite to enable me to understand what had thus been done ; and I had been in habits of intercourse with several of the most eminent men of science of our time, both in our own and in other countries. Having thus lived with some of the great intellects of the past and the present, I had found myself capable of rejoicing in their beauties, of admiring their endowments, and, I trusted, also, of understanding their discoveries and views, their hopes and aims. I did not, therefore, turn aside from the responsibility which the character of the Historian of Science imposed upon me. 'I have not even shrunk from it when it led me into the circle of those who are now alive, and

among

whom we move. For it seemed to me that to omit such portions of the history as I must have omitted to avoid thus speaking of my contemporaries, would have left my work mutilated and incomplete; and would have prevented its forming a platform on which we might stand and look forward into the future. I trusted, moreover, that my study of the philosophers of former times had enabled me to appreciate the discoveries of the present, and that I should be able to speak of persons now alive, with the same impartiality and in the same spirit as if they were already numbered with the great men of the past. Seeking encouragement in these reflections, and in the labour and thought which I was conscious of having bestowed upon my task, I have conducted my history from the earliest ages of the speculative world up to our own days.

To some persons it may appear that I am not

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