DEF 
causes, they shall forfeit their issues, unless 
they have any reasonable excuse proved by 
witnesses, in which case the justices may 
discharge the issues for default. 
DEFENCE, in fortification, all sorts of 
works that cover and defend the opposite 
posts, as flanks, casemates, parapets, and 
faussebrays. See Fortification. 
DEFENDER of the Faith, a peculiar 
title given to the King of England by Pope 
Leo the Tenth to King Henry the Eighth, 
for writing against Martin Luther, in be- 
half of the Church of Rome, then ac- 
counted domiciliiimfidei catholicce. 
DEFERENTIA vasa. See Anatomy. 
DEFICIENT numbers, those whose 
parts or multiples added together, fall short 
of the integer whereof they are the parts ; 
such is 8, its parts, 1, 2, 4, making only 7. 
See Number. 
DEFILE, in fortification, a straight nar- 
row passage, through which a company of 
horse or foot can pass only in file, by mak- 
ing a small front, so that the enemy may 
take an opportunity to stop their inarch, 
and to charge them with so much the more 
advantage, in regard that those in the front 
and rear, cannot reciprocally come to the 
relief of one another. 
DEFINITE, in grammar, is applied to 
an article tliat has a precise determinate 
signification ; such as the article the in Eng- 
lish, le and la in French, &c. which fix and 
ascertain the noun they belong to, to some 
particular, as the King, le Roy ; whereas in 
the quality of King, de Roy, the articles of 
and de mark nothing precise, and are tliere- 
fore indefinite. 
DEFINITION, the shewing the mean- 
ing of one word by several other not sy- 
nonymous terms. The meaning of words 
being only the ideas they are made to stand 
for by him that uses them, the meaning of 
any term is then shewed, or the word is de- 
fined, when by other words, the idea it is 
made the sign of, and is annexed to it in 
the mind of the speaker, is, as it were, re- 
presented and set before the view of an- 
other; and thus its signification is ascer- 
tained. This is the only end and use of de- 
finitions, and therefore the only measure of 
what is, or is not a good definition. 
Tiie names then of simple ideas are inca- 
pable of being defined, because the several 
terms of a definition signifying several 
ideas, they can altogether by no means re- 
present an idea which has no composition 
at all ; and therefore a definition, which is 
properly but shewing the meaning of any 
DEF 
one word by several others, not signifying 
the same each, can in the names of simple 
ideas have no place. Definitions which 
then take place in compound ideas only, 
are of two sorts ; the definition of the name, 
which is the explanation of what any word 
means; and the definition of the things 
which explains in what the nature of that 
thing consists. 
The special rules for a good definition 
are these : 1. A definition must be univer- 
sal, or adequate, that is, it must agree to all 
the particular species, or individuals that 
are included under the same idea. 2. It 
must be proper, and peculiar to the thing 
defined, and agree to that alone. These 
two rules being observed, will always ren- 
der a definition reciprocal with the thing 
defined, that is, the definition may be used 
in the place of the thing defined ; or they 
may be mutually affirmed concerning each 
other. 3. A definition should be clear and 
plain ; and indeed it is a general rule con- 
cerning the definition both of names and 
things, that no word should be used in 
either of them, which has any difficulty in 
it, unless it has been before defined. 4. A 
definition should be short, so that it must 
have no tautology in it, nor any words su- 
perfluous. 5. Neither the thing defined, 
nor a mere synonymous name, should make 
any part of the definition. 
DEFLAGRATION, in chemistry, the 
act of burning two or more substances to- 
gether, as charcoal and nitre. When a 
quantity of nitre, (nitrate of potash), is 
mixed with an equal weight of sulphur, 
charcoal, or other inflammable substance, 
if the mixture is thrown into a crucible 
heated to redness, a very vivid combustion 
is instantly excited : this is deflagration, 
which is thus explained: nitre is a com- 
pound of nitric acid and potash : nitric 
acid consists of nitrogen and oxygen ; the 
nitre, therefore, contains a large portion of 
oxygen, which is in so weak a state of 
combination, that it is separated by expo- 
sure to a red heat. When, therefore, the 
mixture of the nitre, and of the inflamma- 
ble body is thrown into the heated cruci- 
ble, the oxygen of the former is disengaged ; 
it is thus suddenly presented to the inflam- 
mable body, and hence the vivid combus- 
tion that is excited ; and for the production 
of this, it is not even requisite to raise the 
temperature so high as that which would 
be necessary, if applied alone, to decom- 
pose the nitre, the affinity of the inflam- 
mable body to the oxygen of the nitre, 
