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to be cut.

A thing is viscous when, being moist or soft, it is tractile. Bodies

owe this property to the interlocking of their parts when they are

composed like chains, for then they can be drawn out to a great length

and contracted again. Bodies that are not like this are friable.

Bodies are compressible when they are squeezable and retain the

shape they have been squeezed into; incompressible when they are

either inapt to be squeezed at all or do not retain the shape they

have been squeezed into.

Some bodies are combustible and some are not. Wood, wool, bone are

combustible; stone, ice are not. Bodies are combustible when their

pores are such as to admit fire and their longitudinal pores contain

moisture weaker than fire. If they have no moisture, or if, as in

ice or very green wood, the moisture is stronger than fire, they are

not combustible.

Those bodies give off fumes which contain moisture, but in such a

form that it does not go off separately in vapour when they are

exposed to fire. For vapour is a moist secretion tending to the nature

of air produced from a liquid by the agency of burning heat. Bodies

that give off fumes give off secretions of the nature of air by the

lapse of time: as they perish away they dry up or become earth. But

the kind of secretion we are concerned with now differs from others in

that it is not moist nor does it become wind (which is a continuous

flow of air in a given direction). Fumes are common secretion of dry

and moist together caused by the agency of burning heat. Hence they do

not moisten things but rather colour them.

The fumes of a woody body are called smoke. (I mean to include bones

and hair and everything of this kind in the same class. For there is

no name common to all the objects that I mean, but, for all that,

these things are all in the same class by analogy. Compare what

Empedocles says: They are one and the same, hair and leaves and the

thick wings of birds and scales that grow on stout limbs.) The fumes

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