DITR 
of observation; and also for the retreat of 
a garrison, in case of necessity, so that they 
may capitulate with greater advantage. 
DUO, in music, a song or composition 
to b'e performed in two parts only, one 
sung, the other played on an instrument, or 
by two voices. 
Duo is also when two voices sing dif- 
ferent parts, as accompanied with a third, 
which is a thorough bass. It is seldom that 
unisons and octaves are used in duos, ex- 
cept at the beginning and end. 
DUODENUM, the first of the small 
guts, so called from its length, which is 
about twelve fingers breadth. It has its 
origin at the pylorus, or right orifice of the 
stomach ; from which ascending a little, it 
afterwards descends again, and towards its 
end re-ascends, and runs transversely to- 
wards the left kidney : at the distance of 
three or four fingers from the pylorus it re- 
ceives, at one prominent hiatus or mouth, 
the choledochic and pancreatic ducts, which 
discharge their respective liquors into it. 
See Anatomy. 
DUPLICATE, among lawyers, denotes 
a copy of any deed, writing, or account. 
It is also used for the second letters patent, 
granted by the Lord Chancellor in a case 
wherein he had before done the same. Also 
a second letter written and sent to the same 
party and purpose as the former, for fear of 
the first’s miscarrying, is called a dupli- 
cate. 
Duplicate proportion) or ratio, is a ra- 
tio compounded of two ratios; thus, the 
duplicate ratio of a to 6, is the ratio of a a to 
h b, or of the square of a to the square of b. 
Hence the duplicate ratio ought to be well 
distinguished from double. 
In a series of geometrical proportionals, 
the first term to the third is said to be in a 
duplicate ratio of the first to the second ; 
thus in 2, 4, 8, 16, &c. the ratio of 2 to 8 
is duplicate of that of 2 to 4, or as the 
.square of 2 to the square of 4. Duplicate 
ratio is therefore the proportion of squares, 
as triplicate is of cubes, &c. and the ratio 
of 2 to 8 is said to be compounded of that 
of ^ to 4, and of 4 to 8. 
DUPLICATION, in general, signifies 
the doubling of any thing, or multiplying of 
it by 2 : also the folding of any thing back 
again on itself. See Cube. 
DURA mater, one of the membranes 
which surround the brain. See Anatomy. 
DURANTA, in botany, so called in ho- 
nour of Castor Durantes, a genus of the 
Didynamia Angiospermia class and order. 
DUR 
Natural order of Personatas. Vitices, Jus- 
sieu. Essential character : calyx five-cleft, 
superior ; ben-y four-seeded ; seeds two- 
celled. There are three species. These are 
shrubs with quadrangular branches ; the 
flowers are in loose spikes, either from the 
axils, or at the ends of the branches. They 
have generally axillary spines ; and they are 
so much alike in their manner of flowering, 
as well as in the structure and colour of the 
flower, that it is doubtful whether they 
may not be all one species. 
DURATION, an idea which we get by 
attending to the fleeting and perpetually 
perishing part of succession ; the idea of 
succession being acquired by reflecting on 
that train of ideas which constantly follow 
one another in our minds, as long as we are 
awake. The simple modes of duration are 
any different lengths of it whereof we have 
distinct ideas, as hours, days, years, time, 
eternity, &c. Duration, as marked by 
certain periods and measures, is what we 
most property call time. 
Duration of action, according to Ari- 
stotle, is confined to a natural day in trage- 
dy ; but the epopoeia, according to the 
same critic, has no fixed time. 
Duration of an eclip^. See Astro- 
nomy and Eclipse. 
Duration, in botany, the division of 
vegetables into trees, and perennial and 
annual herbs, is founded on the different 
duration of these plants. Trees subsist for 
several years, both by the root and stem : 
perennial herbs lose their stems during the 
winter, and are renewed by the root in 
the following spring : annuals perform the 
changes of vegetation but once, and are 
perpetuated in the seed. Striking as those 
differences are, Linnaeus thinks the duration 
of plants so fallacious, that he never em- 
ploys it as a specific difference. The rea- 
son he assigns is very pertinent. The du- 
ration of plants, he says, is frequently af- 
fected by place or climate, and therefore 
ought not to be regarded as an invariable 
circumstance proper for discriminating the 
species. In the wanner climates, which 
enjoy a perpetual summer, most of the 
plants are perennial, and of the tree-kind ; 
yet many of them, when removed to our 
colder European climates, lose their woody 
texture, and become herbaceous and fre- 
quently annual. Of this the ricinus, or tree 
palma christi, and marvel of Peru, are fami- 
liar instances. 
Indian cress, beet, sweet marjoram, and 
tree-mallow, which, witli us, are annual, 
