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parts of marble, or the spots of white and purple in carnations, agree almost in every respect, except in colour. Whence it is easily collected, that colour does not greatly depend upon the intrinsic nature of the coloured body, but is owing to a somewhat gross, or bare mechanical texture of the parts. Thus these instances are solitary, in point of difference.

And we call both the kinds by one and the same name.

2. Travelling Instances (Instantiae Migrantes).

In the second place come travelling instances, or those wherein the nature inquired after travels, or advances to generation, when it was not before in being; or, on the coutrary, travels, or tends to destruction, when it was in being before. And, therefore, in either correlative, such instances are always duplicate; or rather one instance, in motion, or passage, is continued to the opposite period. And instances of this kind not only accelerate and confirm the business of exclusion, but also drive the affirmation, or form itself, into a narrow compass. For the form of the thing must necessarily be somewhat introduced, or abolished, by this transmigration And, though all exclusion promotes and forwards the affir. mation, yet this is more directly done in the same subject than in different ones ; for it plainly appears, from all we have said before, that the form discovering itself in one thing leads to its discovery in all the rest. But the more simple this passage is, the nobler the instance should be esteemed.

Again, these travelling instances are of great use in practice, because, as they exhibit the form joined with an efficient, or privation, they clearly design or mark out the practical operation in some cases ; whence any easy passage is also afforded to the neighbouring discoveries. There is, however, some danger in these instances, that requires a particular caution ; for they may be apt to restrain the form too much to the efficient, and to infect or at least to tinge the understanding with a false notion of the form, through an apparent mixture of the efficient; whereas the efficient is never more than the vehicle of the form. But this inconvenience is easily remedied by making a just exclusion.

To give an example of a travelling instance : suppose the nature inquired after were whiteness, an instance advancing to generation is glass, whole, and in powder; and again, simple water, and water beat into froth; for whole glass, and simple water, are transparent bodies, not white; but powdered

glass, and the froth of water, are white, not transparent. It comes therefore to be inquired, what has happened to the glass, or water, in this transmigration ; for, it is manifest, that the form of whiteness travels, or is conveyed over by pounding the glass, and agitating the water ; but nothing is here found added, besides a bare comminution of the parts of the glass and the water, together with the interposition of the air. And it is no small acquisition in discovering the form of whiteness, that two bodies, of themselves more or less transparent, viz. air and water, or air and glass, being mixed together, in subtile or small parts, should exhibit whiteness, by differently reflecting the rays of light.

We must also give an example of the danger, and caution, above mentioned ; for it may here readily occur to the understanding, depraved by these kinds of efficients, that air is always necessary to the form of wbiteness, or that whiteness is generated only by transparent bodies, which two positions are absolutely false, and rejected by numerous exclusions. It will rather appear, without the interposition of the air, &c. that the bodies perfectly uniform, or similar, in their optical parts, prove transparent: that those which have the simple texture, or arrangement of their parts disturbed, are white; that a dissimilarity in the regular rexture of bodies affords all colours, except black; and that a dissimilarity in a compound, absolutely irregular, and confused texture, constitutes black

And, for an instance advancing to destruction in the same nature of whiteness, we have it in froth subsided, or snow dissolved; for water deposits its whiteness, and puts on transparency, upon becoming entire, without any intermixture of air,

We must by no means omit, that under travelling instances should be comprehended, not only those which travel to absolute generation and privation, but such likewise as travel to a greater or less degree of the nature sought, since these also tend to the discovery of the form, as plainly appears both from the definition of a form, ahove laid down, and the table of comparison. And therefore the instance of paper, which is white when dry, but proves less white when wet, and comes pearer to the state of transparency, upon the exclusion of the air, and the reception of the water, is of the same use as the instances above mentioned.

ness.

3. Forthshowing Instances (Instantiae Ostensivae);

called also Blazings (Elucescentiae) and Liberated and Predominant Instances. It is as an example of these instances that the Thermometer is introduced, under the name of vitrum calendare aëris, which should mean the calendar glass of the air, but which Bacon probably intended to signify the glass for measuring the heat of the air, under the notion that calendare was a derivative of caleo.*

4. Clandestine or Twilight Instances, which are the opposite of the preceding.–

For example ; let the nature inquired into be consistence or solidity, the contrary of which is liquidity or fluidity, then clandestine instances are such as exhibit some faint and low degree of consistency in a fluid ; suppose a bubble of water, which is a kind of consistent and determinate pellicule, made of the body of the water. In like manner icicles, if there be water to follow them, lengthen themselves out in a very slender thread, to prevent a discontinuity of the water; but it there be not a sufficient quantity to follow, the water then falls in round drops, which is the figure that best supports it against discontinuation; and at the very instant when the thread of water ends, and the falling in drops begins, the water recoils upwards to avoid being discontinued. So in metals, which are fluid upon fusion, though a little tenacious, some of the melted mass frequently springs up in drops, and sticks in that form to the sides of the crucible. There is a like instance in the looking-glasses, commonly made of spittle by children, in a loop of rush or whalebove, where we find a consistent pellicule of water. But this is observed to much better advantage in that other diversion of children when they take strong soapy water, and blow in it with a pipe, so as to raise the water into a tower or castle of bubbles, whilst by the interposition of the air, the soapy water becomes consistent to that degree as to be thrown a considerable distance without breaking. This also appears

* Shaw translates it the weather-glass, which would now be understood to mean the barometer, an instrument not invented in Bacon's day; but the thermometer also was formerly called the weather-glass. Thus Dryden writes :

As in some weather-glass my love I hold,
Which falls or rises with the heat or cold.

to advantage in froth and snow, which put on such a consistency, that they may be almost cut with a knife, though they are hut bodies formed of air and water, both of them fluid. These several instances seem clearly to intimate that fluidity and consistency are no more than vulgar notions relative to the human sense, and that all bodies have a real appetite to avoid discontinuation, though in homogeneous bodies, such as fluids are, it is but weak and feeble, whilst in those compounded of heterogeneous matters, it proves more strong and powerful, because the application of what is heterogeneous binds bodies up, but the entrance of what is homogeneous relaxes and dissolves them.

As a farther example; if the nature sought were attraction, or the appetite of approach in bodies, a most remarkable glaring instance, as to the discovery of the form, is the loadstone. The contrary of an attractive nature is an unattractive nature, though in a similar substance; as in iron, which does not attract iron; nor does lead attract lead, nor wood attract wood, nor water attract water. But the loadstone armed with iron, or rather the iron of an armed loadstone, is a clandestine instance; for here it happens, that an armed loadstone does not, at a certain distance, attract iron stronger than an unarmed loadstone ; but if the iron be moved so near as to touch the iron of the armed loadstone, then the armed loadstone will support a much greater weight of iron, than the naked and unarmed loadstone, by reason of the similitude of substance betwixt iron and iron, which operation was altogether clandestine and secret, or concealed in the iron before the loadstone was applied. Whence it is manifest, that the form of attraction is a thing that is vivid and strong in the loadstone, but weak and latent in iron.

After the same manner, it is observed, that headless arrows of wood, being fired out of a gun, will penetrate farther into wood, or the sides of a ship, than the same arrows headed or pointed with iron, by reason of the similitude of substance betwixt wood and wood, though this before lay concealed the wood.

Again; though air does not manifestly attract air, nor water manifestly attract water, in a state of entireness, yet one bubble approaching another makes it easier dissolve, than if the other bubble were away, by reason of the appetite of conjunction between water and water, and between air and air.

And this kind of clandestine instances, which, as we before observed, have a noble use, are most remarkable in the small

and subtile parts of bodies, because the greater masses of things follow the more general and universal forms.

5. Constituent, or Handfilling (Manipulares) Instances :

For example, let the nature sought be memory, or the means of exciting and helping the memory; the constituent instances will here be, first, order, or distribution, and places for artificial memory. Order, or distribution, mavifestly assists the memory; and places for artificial memory may either be places in a proper sense, as a door, a window, a corner, &c., or familiar and known persons; or any other things at pleasure; provided they be placed in a certain order; as animals, plants, words, letters, characters, historical personages, &c., though some of these are more, and some less fit for the purpose. But such kind of places greatly help the memory, and raise it far above its natural powers. Again; verse is easier learnt and remembered than prose.

And this collection, or packet, of the three above-mentioned instances, viz. order, artificial place, and verse, constitute one species of help for the memory: and this species of help may be justly called the prevention of endless search. For when a person endeavours to recollect, or call a thing to mind; if he has no previous notion or perception of what he is in quest of, he casts about, and tries every track, as it were without end : but if he has any previous notion, this infinity of search is presently cut short; and the memory is brought to hunt nearer home. But in the three instances above mentioned, there is a clear and certain previous notion contained. For in the first, there is required somewhat agreeable to order; in the second, an image is required, that has some agreement, or relation, to those fixed places; in the third, words that will stand in verse: so that intinity is thus cut off or prevented, and the search limited and restrained.

Other instances will give this second species; that whatever brings an intellectual thing to strike the sense (which is the method principally used in artificial memory), helps the remembrance.

Other instances will give this third species; that those things which make an impression by means of a strong affection or passion, as by causing fear, surprise, blushing, delight, &c., assist the memory.

Other instances will give this fourth species ; that those

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