Of the second kind of instantie soktarie, Bacon mentions the white or coloured veins 'which occur in limestone or marble, and yet hardly differ in substance or in structure from the ground of the stone. He concludes, very justly, from this, -that colour has not much to do with the essential properties of body.
II. The instantly naigrantes exhibit some nature or property of body, passing from ono condition to another, either from less to greater, or from greater to less ; arriving newer perfection in the first case, or verging towards extinction in the second.
Suppose the thing inquired into were the cause of whiteness in bodies; an instantiO mi. grans is found in glass, which, when entire, is without colter, hut, when pulverized, be. domes white. The same is the case with water unbroken, and water dashed into foam. In both cases,- the separation into particles produces whiteness. So also the communica tion of fluidity to metals by the application of, heat ; and the destruction of that fluidity by the abstraction of heat, are examples of both kinds of the hulas:tie migrans. laskaa ceo of this kind are very powerful for reducing the cause inquired after inter a min"' space, and for removing all the accidental circumstances. It is necessary, however, 14 Ba. con I very justly remarks, that we should consider not merely the case when a certain coa. is lost, and another produced, but the gradual changes made in those qualities durbig their migration, via. the increase of the one, and the corresponding diminution of the other. The quantity which changes proportionally to another, is connected with it either as cause and effect, or se a collateral effect of the same cause. -When, again, we find two qualities which do not increase proportionally, they afford a negative instance, and mauve ns that the two are not connected simply as cause and effect.
The mineral kingdom is the great theatre of the instantice migrantes, where the same noture is seen in all gradations, from the most perfect state, till it become entirely evanes lent. Such are the .shells which we see so perfect in figure and structure in limestone, and gradually losing themselves in the finer marbles, till they can no longer be distinguish; ed. The use, also, of one such .fact to explain or interpret another, is nowhere so well,
seen as in the history of the mineral kingdom.
III. In the third place are the instantia ostensive', which Bacon also calls elucescentice predominantes. They are the facts which show some particular nature in its highest state of power and energy, when it is either freed from the impediments which usually eonnteract it, or is itself of such force as entirely to repress those impediments. For as every body is susceptible of many different conditions, and has many different forms com bined in it, one of them often confines, depresses, and hides another entirely, so that it is not easily distinguished. There are found, however, some subjects in which the nature inquired into is completely displayed, either by the absence of impediments, or by the pre. dominance of its own power..