Our Science has been built on the labours of scientific men in past ages.  New generalisations imagined by one thinker, new crucial experiments devised by another, new instruments of observation invented by another,—­these have been the steps by which Science has grown and established its authority and enlarged its dominion.  When or by whom the first steps were made we have no record.  No mathematician that ever lived showed greater natural power of intellect than he, whoever he was, who first saw that the singular contained the universal; but we know neither his name nor his age, nor his birthplace nor his race.  But after those first steps had been taken, we know who have been the leaders in scientific advance.  And we know what they have done, and what they are doing; and we can conjecture the direction in which further advances will be made.  And so we can trace the development of this kind of knowledge, and in a certain and very real sense this development may be called an evolution.

But there is this difference between the evolution of nature and the evolution of the science of nature.  The evolution of nature results in the existence of forms which did not exist before; the evolution of knowledge results in the perception of laws which were already in existence.

The knowledge grows, but the things known remain.  The knowledge is not treated as if independent of the things known or believed to be known, as a phenomenon belonging merely to the human mind, with beginnings and laws and consequences and history of its own.  And, consequently, its having a regular growth is not used as an argument against its substantial truth.

The Science of Mathematics, for instance, has a history; but no mathematician will admit that the fact that it has a history affects its claims to acceptance as truth.  We may ask, how men have been brought to believe the deductions of the higher mathematics, and we may answer our own question by tracing the steps; but our conviction is not shaken that these deductions are true.

And so, too, we can trace the steps by which the great generalisations of Science have been reached, and we may show that Kepler grew out of Copernicus, and Newton out of Kepler; but the proof that the knowledge of one truth has been evolved out of the knowledge of another, and that out of the knowledge of another, is not used to show that all this Science has nothing to do with truth at all, but is only a natural growth of human thought.  Science has grown through all manner of mistakes—­mistakes made by the greatest thinkers and observers, mistakes which men ignorantly laugh at now, as their own mistakes will be no doubt laughed at in turn hereafter.  But we do not, therefore, treat scientific thought as nothing more than one of the phenomena of humanity; ways of thinking which necessarily grew out of the conditions in which men have existed, but sufficiently accounted for by their origin and mode of growth having been shown, and having no solidity of their own.