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yet, by an exact scrutiny, some medium may perhaps be found to deaden this virtue more than any other medium, comparatively and in some degree.

Thus suppose the loadstone would not attract iron so much through gold of a certain thickness, as through the same space of air; or not so much through ignited silver, as through the same when cold, &c. For we have not made the trials, but it is sufficient to propose them by way of example *.

In like manner, there is no body found here upon the earth but what is susceptible of heat, when applied to the fire; yet air receives heat much sooner than a stone. And such is the substitution made in the way of degree or approximation.

The substitution by analogy is useful, but less certain, and therefore to be practised with judgment. This is performed when an insensible thing is brought down to the sense; not by the sensible operations of the insensible body itself, but by considering some other sensible body of kin thereto.

For example; if the subject of enquiry were the mixture of spirits, which are invisible sub-` stances, we are here to observe, that there seems

See below, Aph. 43.

to be a certain affinity between bodies, and the matter that feeds or nourishes them. Thus oil and fat bodies seems to be the food of flame; and water and aqueous bodies, the food of air; for flames multiply themselves upon the exhalations of oil; and air upon the vapour of water. In this enquiry, therefore, we may consider the mixture of water and oil, which is manifest to the sense, though the mixture of air and flame is not perceptible. Now, oil and water are very imperfectly mixed together by composition, or agitation; but more curiously and elaborately in. plants, blood, and the parts of animals, and, therefore, something of the like kind may happen as to the mixture of flame and air in un-1 tangible bodies. For, though flame and air do not well incorporate by simple motion, yet they seem to mix in the spirits of plants and animals; the rather, because all animal spirits prey upon both kinds of moisture, viz. the aqueous, the unctuous, as its aliment*.

In like manner, if the subject of enquiry be not the perfect mixture of pneumatical or untangible bodies, but only their composition; viz. whether they will easily mix among themselves; or rather, suppose, for example, certain winds,

See the Axioms at the close of the History of Life and Death. See also Mr. Boyle's Experiments to this purpose. Abridgm. Vol. II. p. 469.


or exhalations, or other pneumatical bodies, which mix not with common air, but only lodge and float therein, under the form of globules and drops, as being rather broke and ground by the air, than received into and incorporated with it. Now this cannot be perceived by the sense, either in common air, or other pneumatical bodies, by reason of their subtilty or fineness; but a certain image or representation may be had of the thing, with regard to its possibility, in tangible fluids; such as quicksilver, oil, water, and even in air itself, when it is broke and dissipated, or rises in small particles or bubbles through water; and again, an image of it may be had in the grosser fumes +; and lastly, in dust raised and floating in the air in all which cases there is no incorporation made. And this representation is not faulty, provided it be first carefully examined, whether among pneumatical bodies there may be such an heterogeneity as is found among liquors; for in case there is, then these representations by analogy may be commodiously substituted .

These being heterogeneous fluids, and not mixing together upon shaking.

Which do not incorporate with the air.

+ See Mr. Boyle upon the different surfaces of fluids in contact. Abridgm. Vol. I. p. 316-318. and 388-396.

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And though, as we before observed, information is to be derived from these supplemental instances, by way of refuge or recourse, when proper instances are wanting; yet we would have it understood, that they are also of great use, even when the proper instances are procurable; particularly in strengthening the information, with the assistance of those. But the time for treating of these instances more exactly is when we come, by the law of order, to the helps of induction *.

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43. In the twentieth place come lancing instances, which we also, for a different reason, call by the name of vellicating instances. We call them vellicating instances, because they twitch the understanding; and lancing instances, because they cut or lance through nature; whence we also call them democritical instances; that is, such as remind the understanding of the admirable and exquisite subtilty of nature, so as to excite and awaken it to attention, observation, and proper enquiry.

For example; the following are lancing or vellicating instances. (1.) That so small a drop of ink in a pen should be drawn out into so many

* A part of the Novum Organum that is wanting. See above, Part II. Aph. 21.

+ Alluding to the Atoms of Democritus. See the Author's Essay upon the Corpuscular Philosophy.

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letters or lines, as we find it; (2.) that silver gilt upon its external surface, should be drawn to such a vast length of gilded wire; (3.) that so very small a worm as that found in the skin, should have a spirit, and a peculiar structure and organization of different parts; (4.) that a little saffron should tinge a whole hogshead of watert: (5.) that a little civet or musk should fill a large chamber with its odour; (6.) that such a great cloud of smoke should be raised from a little incense; (7.) that the exact differences of sounds should be every way conveyed through the air, and even through the holes and pores of wood and water, (though much weakened, indeed, in the passage,) and be reflected with great distinctness and velocity; (8.) that light and colour should so suddenly pass through such a bulk of solid matter, as glass, or of a fluid, as water; yet so as at the same time to convey a great and exquisite variety of images, even though the light suffers refraction and reflection; (9.) that the loadstone should operate through all kinds of bodies, even the most compact and solid; and what is still more wonderful; (10.) that in all these cases the action of one thing does not greatly hinder the action of another, in a neu

* See Mr. Boyle upon Effluvia, Abridgm. Vol. I. p. 485. + See Mr. Boyle upon Effluvia, &c. Vol. I. p. 397, 438.

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