502 
D E N 
DEN 
black. 1 he most esteemed dendrites are 
those found in agates ; and more particularly 
in the sardonyx, cornelian, and other pre- 
cious stones, brought from the East, and 
winch are commonly denominated Moka 
stones. I he Oriental agates display the most 
varied and beautiful forms. Sometimes they 
exhibit the appearance of terraces covered 
with different species of moss, interspersed 
with plants of the fern-tribe, having large 
leaves, and the outlines exquisitely finished : 
the colours are likewise extremely brilliant. 
r Ihese colours are supposed to be owing to 
metallic oxides; others are of a different, and 
perhaps of a bituminous nature. The first 
are dissolved, and wholly disappear, on im- 
mersing the stone in any of the mineral acids; 
while the others resist their action in a 
greater or less degree. Some naturalists 
suppose that dendrites are owing to metallic 
solutions, or other colouring matters, finding 
their way through the pores of the stone, and 
being afterwards forced into the; smallest fis- 
sures by a mechanism similar to that by 
which fluids ascend in capillary tubes. But a 
careful examination of the structure and 
disposition of dendrites, must evince this opi- 
nion to be merely hypothetical ; as the prin- 
cipal branches, in diverging from the com- 
mon stem, observe a great regularity; they 
are nearly parallel to one another on each 
side, and always proceed in one direction, 
like the stems and branches of a real tree ; a 
circumstance inconsistent with the supposi- 
tion of capillary attraction, which extends 
equally in all directions. 
The same observation is equally applicable 
to micaceous dendrites, which are frequently 
found in the granite of the Pyrenees. These 
dendrites, which greatly resemble bunches of 
ostrich feathers, are certainly neither the effect 
of chance, nor of capillary attraction, but of 
a principle much more active than that by 
which simple crystallization is produced. 
A species of metallic dendrites is some- 
times formed by means of lire. For example, 
some kinds of copper ore, on being subjected 
to the action of heat, and afterwards with- 
drawn from the furnace, appear covered with 
brilliant yellow spots, some inches in diame- 
ter, exactly resembling in form lichens grow- 
ing on r®cks. These arborizations, which 
are of pure copper, are very singular ; being 
composed of vertical threads, of about a line 
in height, united in fasciculi, like so many 
small sheaves standing upright by the side of 
each other. The finest specimens of this 
kind of metallic dendrites are produced at a 
foundry on the Oural mountains. The ore 
with which this foundry is supplied, is 
brought from the mines of Touria, where the 
most beautiful native copper in a state of 
vegetation yet known, is to be found. In 
whatever manner we may be inclined to ac- 
count for this wonderful phenomenon, it 
should seem, from the above fact, that the 
same cause which produces these arboriza- 
tions in the mine, must likewise produce the 
same effect after the ore has been subjected 
to the action of fire. See Plate Nat. Hist, 
figs. 160 and 16 1. 
DEN DROME I ER, from SevSpty a tree, 
and (x I measure, an instrument invent- 
ed by Messrs. Buncombe and Whittel, for 
which they obtained a patent, so called from 
its use in measuring trees. It consists of 
a semicircle A, plate Miscel. fig. 37 and 38, 
divided into two quadrants, and graduated 
from the middle; upon the diameter B there 
hangs a plummet L for fixing the instrument in 
a vertical position; there are also a chord B 
parallel to the diameter, and a radius E 
passing at right angles through the diameter 
and chord. From a point on the radius hangs 
an altimeter C, between the chord and diame- 
ter, to which are fixed a small semicircle G, 
and a screw, to confine it in any position. 
1 he altimeter, which is contrived to form the 
same angle with the radius of the instrument 
| as the tree forms with the horizon, is divided 
I ‘ rom * ts ventre both ways into forty equal 
parts ; and these parts are again divided into 
halves and quarters. Upon the small semi- 
circle G, on which is accounted the quantity 
of the angle made by the altimeter and ra- 
dius, are expressed degrees from 60 to 120 
being 30 on each quadrant. The radius is 
numbered with the same scale of divisions as 
the altimeter. 1 here is also a nonius to the 
small semicircle, which shows the quantity of 
an angle to every five minutes. On the back 
of the instrument the stock M (fig. 38) of the 
sliding piece is confined to the axis N, which 
moves concentrically parallel to the elevation 
index b ou tlie opposite side, to which it is fix- 
ed. d his index is numbered by a scale of 
equal divisions with the altimeter and radius. 
At the end of the index is a nonius, by which 
the angles of elevation above, or of depression 
below, the horizon, measured upon the semi- 
circle of the instrument, are determined to 
every five minutes. There is also a groove 
in the radius, that slides across the axis by 
means of a screw I, working between the 
chord and semicircle of the instrument ; and 
this screw is turned by the key O. Upon 
the stock M is a sliding piece P, that always 
acts at right angles with (he altimeter, by 
I'oove in the I.iHpi- UV. 
DEN 
DENEB, an Arabic term, signifying tail, 
used by astronomers to denote several fixed 
stars. Thus deneb elecet, signifies the bright 
star in the lion’s tail ; deneb adigege, that 
in the swan’s tail ; & c. 
means of a groove in the latter. To the 
shank of the sfiding piece is affixed a move- 
able limb Q,' which forms the same amde 
witu the altimeter as the bough forms with 
the body or trunk of the tree. This limb 
may be of any convenient length, divided 
into equal parts of the same scale with all 
the foregoing divisions. At the extremity of 
the fixed axis, on a centre, an index H, with 
telescopic sights, works horizontally upon the 
moveable limb of the sliding piece. Upon 
tins horizontal index R may be fixed a small 
quad] ant I, described with any convenient 
radius from the centre on which the index 
moves, and divided into 90 degrees, begin- 
ning at a right line drawn from the centre at 
right angles with the fiducial edge of the said 
index ; and upon the extremity of the axis 
is a nonius, whereby to determine the quan- 
tity of an angle upon the quadrant every 
aites. There are also two small semi- 
live minutes 
. iUUU II OC 1111“ 
circular arches S, S, serving to keep the 
sights in a parallel position, each containing' 
an equal number of degrees. Upon these 
arches is measured the angle subtending' a 
side equal to the difference of the altitudes 
ot ihe observed objects above the plane of 
the horizon, and whose base is the nearest 
distance between the perpendiculars in which 
these objects are situated. I lie dendrometer 
is fitted to a theodolite ; and may be used 
eithei with or without it, as occcasion re- 
quires. 
I he principal use of this instrument is for 
measuring the length and diameter of any 
tree, perpendicular or oblique to an hori- 
zontal plane, or in any situation of the plane 
on which it rests, or of any figure, whether 
regular or irregular, and also the length anti 
diameter of the boughs, by mere inspection ; 
and the inventors of it have calculated 
tables, annexed to their account of the in- 
strument itself, by the help of which the 
quantity of timber in a tree is obtained with- 
out calculation, or the use of the sliding rule 
I he instrument is rectified by setting it in a 
perpendicular position, by means of the plum- 
met, and screwing it to the staff; then the' 
altimeter is placed in the exact position of 
the tree, whether perpendicular, reclining 
or inclining, and screwed fast. If the tree 
stands on level ground, the horizontal dis- 
tance from the tree to the axis of the inst ru- 
ment is measured with a tape-line, and the 
radius is moved with the kev till that distance 
be cut upon it by the inside of the diameter ; 
but it the ground be slanting, the distance 
from the tree to the instrument is measured, 
and the elevation index is moved till the point 
ot the tree from which the distance was mea- 
sured is seen through the sights, and there 
screwed tast; and the radius is moved back- 
wards or forwards with the key, till this dis- 
tance is cut upon the elevation index by the 
perpendicular line of the altimeter; and the 
horizontal line will be marked upon the ra- 
dius by the inside ot the diameter. In order 
to obtain the length of the tree, the elevation 
index is first moved downwards, till the bot- 
tom of the tree cut by the horizontal wires is 
observed through the sights, and the feet and 
inches marked by the index upon the alti- 
meter below the 'point of sight or horizontal 
line are noted down; then the index is moved 
upwards till the part to which you would 
measure, cut by the horizontal wires, is seen, 
and the ieet and inches marked on the alti- 
meter above the point of sight are noted • 
tiiese two quantities added together give the 
exact length ot the tree, which is inserted in 
a field-book. For the girth of the tree, the 
circumference in that part where the hori- 
zontal distance was taken, is measured with 
the tape-line; and a sixth part of this circum- 
ference is added to the distance on the ra- 
dius, which was before cut by the inside of 
the diameter, because the tape-line, in taking 
the distance, cannot be applied to the centre 
of the body of the tree; then the elevation 
index is lowered to that part of the tree of 
which the diameter is to be taken, and 
screwed fast. Set the moveable limb of the 
s iding piece quite straight, and the edge of 
the horizontal index upon the. first division of 
, • / urn tIie whole instrument about to the 
el hand, till you see through the sights the 
left side of the tree cut exactly by the per- 
pendicular wires; then, the instrument bein<» 
fixed, move the sights only upon the sliding 
piece till you see the right side of the tree 
cut also by the perpendicular wires; and you 
will find the true diameter marked by the ho- 
rizontal index upon the sliding piece. Which 
is to be entered in a distinct column of the 
field-book. 
for the boughs. Let the distance on the 
radius be now reduced to its former quantity. 
