In that he shows, with great logical skill, as well as with some humour, how the man who, on rising in the morning, finds the parlour window open, the spoons and teapot gone, the mark of a dirty hand on the window-sill, and that of a hob-nailed boot outside, and comes to the conclusion that some one has broken open the window and stolen the plate, arrives at that hypothesis--for it is nothing more--by a long and complex train of inductions and deductions, of just the same kind as those which, according to the Baconian philosophy, are to be used for investigating the deepest secrets of Nature. This is true, even of those sciences which involve long mathematical calculations. In fact, the stating of the problem to be solved is the most important element in the calculation; and that is so thoroughly a labour of common sense that an utterly uneducated man may, and often does, state an abstruse problem clearly and correctly; seeing what ought to be proved, and perhaps how to prove it, though he may be unable to work the problem out, for want of mathematical knowledge. But that mathematical knowledge is not--as all Cambridge men are surely aware--the result of any special gift. It is merely the development of those conceptions of form and number which every human being possesses; and any person of average intellect can make himself a fair mathematician if he will only pay continuous attention; in plain English, think enough about the subject. There are sciences, again, which do not involve mathematical calculation; for instance, botany, zoology, geology, which are just now passing from their old stage of classificatory sciences into the rank of organic ones. These are, without doubt, altogether within the scope of the merest common sense. Any man or woman of average intellect, if they will but observe and think for themselves, freely, boldly, patiently, accurately, may judge for themselves of the conclusions of these sciences, may add to these conclusions fresh and important discoveries; and if I am asked for a proof of what I assert, I point to 'Rain and Rivers,' written by no professed scientific man, but by a colonel in the Guards, known to fame only as one of the most perfect horsemen in the world. Let me illustrate my meaning by an example. A man--I do not say a geologist, but simply a man, squire or ploughman--sees a small valley, say one of the side-glens which open into the larger valleys in the Windsor forest district. He wishes to ascertain its age.