century, that they recognised but one scientific method, applicable alike to man and to nature, we find this notion of the existence of a broad distinction between nature and man in the writings both of Bacon and of Hobbes of Malmesbury; and I have brought with me that famous work which is now so little known, greatly as it deserves to be studied, “The Leviathan,” in order that I may put to you in the wonderfully terse and clear language of Thomas Hobbes, what was his view of the matter.  He says:—­

“The register of knowledge of fact is called history.  Whereof there be two sorts, one called natural history; which is the history of such facts or effects of nature as have no dependence on man’s will; such as are the histories of metals, plants, animals, regions, and the like.  The other is civil history; which is the history of the voluntary actions of men in commonwealths.”

So that all history of fact was divided into these two great groups of natural and of civil history.  The Royal Society was in course of foundation about the time that Hobbes was writing this book, which was published in 1651; and that Society was termed a “Society for the Improvement of Natural Knowledge,” which was then nearly the same thing as a “Society for the Improvement of Natural History.”  As time went on, and the various branches of human knowledge became more distinctly developed and separated from one another, it was found that some were much more susceptible of precise mathematical treatment than others.  The publication of the “Principia” of Newton, which probably gave a greater stimulus to physical science than any work ever published before, or which is likely to be published hereafter, showed that precise mathematical methods were applicable to those branches of science such as astronomy, and what we now call physics, which occupy a very large portion of the domain of what the older writers understood by natural history.  And inasmuch as the partly deductive and partly experimental methods of treatment to which Newton and others subjected these branches of human knowledge, showed that the phenomena of nature which belonged to them were susceptible of explanation, and thereby came within the reach of what was called “philosophy” in those days; so much of this kind of knowledge as was not included under astronomy came to be spoken of as “natural philosophy”—­a term which Bacon had employed in a much wider sense.  Time went on, and yet other branches of science developed themselves.  Chemistry took a definite shape; and since all these sciences, such as astronomy, natural philosophy, and chemistry, were susceptible either of mathematical treatment or of experimental treatment, or of both, a broad distinction was drawn between the experimental branches of what had previously been called natural history and the observational branches—­those in which experiment was (or appeared to be) of doubtful use, and where, at that time, mathematical methods