A retrospect of the history of human knowledge offers to our contemplation few things of deeper interest than the evidence it so repeatedly affords of some great law which regulates the gradual development of truth, and determines the Progress of Discovery. Although knowledge has, at times, appeared to exhibit something of uniformity in its advances, yet it cannot have escaped the least observant that, as a whole, the Progress of Science has been marked by very variable activity—at one time, marvellously rapid; at another, indefinitely slow; now merged in darkness or obscurity; and now blazing forth with meridian splendour. We observe a series of epochs divided by intervals of great apparent irregularity—intervals which we can neither calculate nor explain; but which, nevertheless, exhibit a periodicity, which the very irregularity serves to render striking and impressive. We may remark, also, a peculiar fitness in the minds of those to whom the enunciation of truth has been successively entrusted: a fitness, not merely for the tasks which have been assigned to each, as the special mission of the individual, but also in the relations of different minds to each other. This adaptation to ends which individual minds have unconsciously combined to accomplish, might be illustrated by many examples, from the earliest records of antiquity, down to our own times. This would be incompatible with our present purpose. We will therefore only refer to one or two illustrations, which, as being familiar, will serve to show what we mean, and to lead us, not unnaturally, to our more immediate object. We cannot contemplate men like Bacon, Galileo, and Kepler, for example, without feeling how auspicious the precession of such minds must have been to the development of the genius of Newton[1]. Newton was born the same year that Galileo died. There is something very interesting and significant too in the peculiar powers of Kepler. Prolific in suggestion, great in mathematical ability, elaborate in analysis, and singularly truthful in spirit, Kepler exemplified two things. These, though very distinct from each other, were both equally instructive; both alike suggestive of the link he represented in the chain of progress. In the laws he discovered, he showed the harvest seldom withheld from the earnest search for truth; but the enormous labour of the mode in which he conducted his researches, as well as the limits prescribed to his discoveries, exemplify the evils which, even in a man of the greatest power, result from proceeding too much on hypothesis. Now it is interesting to remember that this was coincident with the dawning of that glorious light, the Inductive philosophy of Bacon, and shortly succeeded by the splendid generalization of Newton.