Negative instances, or those where the given form is wanting, are also to be collected.
That glass, when pounded, is not transparent, is a negative fact, and of considerable im portance when the form of transparency is inquired into ; also, that collections of vapour, such as clouds and fogs, have not transparency, are negative facts of the same kind. The facts thus collected, both affirmative and negative, may, for the sake of reference, be re duced into tables.
Bacon exemplifies his method on the subject of Heat ; and, though his collection of fasts be imperfect, his method of treating them is extremely judicious, and the whole dis quisition highly interesting.* He here proposes, as an experiment, to try the reflection of the heat of opaque bodies. 3 He mentions also the vitrum calendars, or thermometer, which was just then coming into use. His reflections, after finishing his enumeration of facts, show how sensible he was of the imperfect state of his own knowledge.* After a great number of exclusions have left but a few principles, common to every case, one of these is to be assumed as the cause ; and, by reasoning from it synthetically, we are to try if it will account for the phenomena.
So necessary did this exclusive process appear to Bacon, that he says, " It may perhaps be competent to angels, or superior intelligences, to determine the form or essence direct ly, by affirmations from the first consideration of the subject. But it is certainly beyond the power of man, to whom it is only given to proceed at first by negatives, and, in the last place, to end in an qffirmative, after the exclusion of every thing else." The method of induction, as laid down here, is to be considered as applicable to all in vestigations where experience is the guide, whether in the moral or natural world. " Some may doubt whether we propose to apply our method of investigation to natural philosophy only, or to other sciences, such as logic, ethics, politics. We answer, that we mean it to be an applied. And as the common logic, which proceeds by the syllogism, belongs not only to natural philosophy, but to all the sciences, so our logic, which proceeds by induc tion, embraces every thing."' Though this process had been pursued by a person of much inferior penetration and sagacity to Bacon, he could not but have discovered that all facts, even supposing them truly and accurately recorded, are not of equal value in the discovery of truth. Some
of them show the thing sought for in its highest degree, some in its lowest ; some exhi bit it simple and uncombined, in others it appears confused with a variety of circum stances. Some facts are easily interpreted, others are very obscure, and are understood only in consequence of the light thrown on them by the former. This led our author to consider what he calls Prerogative Instantidrunt, the comparative value of facts as means of discovery, or as instruments of investigation. He enumerates twenty-seven different species, am". enters at some length into the peculiar properties of each. I must content myself, in this sketch, with describing a few of the most important, subjoining, as illustra tions, sometimes the examples which the author himself has giien, but more frequently such as have been furnished by later discoveries in science.
I. The first place in this classification is assigned to what are called instanter solitari•, which are either examples of the same quality existing in two bodies, which have nothing in common but that quality, or of a quality differing in two bodies, which are in all other respects the same. In the first instance, the bodies differ in all things but one ; in the second, they agree in all but one. The hypotheses that in either case can be entertained, concerning the cause or form of the said quality, are reduced to a small =saber ; for, in the first, they can involve none of the things in which the bodies differ ; and, in the se cond, none of those in which they agree.
Thus, of the cause or firm of colour now inquired into, instantly solitaries are found in crystals, prisms of glass, drops of dew, which occasionally exhibit colour, and yet have nothing in common with the stones, flowers, and meta* which possess colour permanently, except the colour itself. Hence Bacon that colony is nothing else than a mo dification of the rays of light, produced, in the first case, by the different degrees of inci dence ; and, in the second, by the texture or constitution of the surfaces of bodies. He may be considered as very fortunate in fixing on these examples, for it was by means of them that Newton afterwards found out the composition of light.