924 HOR 
HOR 
HOR 
fruit is a plum, with a trilocular kernel. 
There is only one species, the tinttoria, a na- 
tive of Carolina. 
HORARY, or Hour-circle. See Use 
of the Globe. 
Horary circles, or lines. See Di- 
alling. 
Horary motion of the earth, the arch 
it describes in the space of an hour, which is 
nearly 15 degrees, though not accurately so, 
as the earth moves with different velocities, 
according to its greater or lesser distance from 
the sun. 
IIORDEUM, barley, a genus of the tri- 
andria-trigynia class of plants, the corolla 
whereof consists of two valves ; the inferior 
yalve is angular, of an ovato-acuminated 
figure, bellied, and longer than the cup, and 
terminates in a very long arista ; the anterior 
valve is lanceolate^, plane and smaller; the 
corolla serves as a pericarpium, surrounding 
the seed, and not letting it out; the seed is 
oblong, ventricose, pointed at each end, and 
marked with a longitudinal furrow. See 
Husbandry. 
HORIA, in entomology, a genus of the 
coleoptera order. Antenna; moniliform; feel- 
ers four, thicker towards the tip ; lip linear, 
rounded at the end. There are two species ; 
the testacea, and the dermestoides. 
HORIZON. See Astronomy and Geo- 
graphy. 
HORIZONTAL dial. See Dialling. 
Horizontal line. See Perspective. 
Horizontal plane, that which is paral- 
lel to the horizon of the place, or nothing in- 
clined thereto. The business of levelling is 
to iind whether two points are in the horizon- 
tal plane, or how much the deviation is. 
Horizontal range of a piece of ord- 
nance, is the distance at which it falls on or 
strikes the horizon, or on a horizontal plane, 
whatever is the angle of elevation or direction 
of the piece. When the piece is pointed pa- 
rallel to the horizon, the range is then called 
the point-blank or point-blanc range. 
The greatest horizontal range, in the para- 
bolic theory, or in a vacuum, is that made 
with the piece elevated to 45 degrees, and is 
equal to double the height from which a 
heavy body must freely fall to acquire the 
velocity with which the shot is discharged. 
Thus, a shot being discharged with the velo- 
city of v feet per second ; because gravity ge- 
nerates the velocity 2g or 32 *. feet in the 
first second of time, by falling 16^ or g feet, 
and because the spaces descended are as the 
squares of the velocities, therefore as 4f ‘ v 2 • • 
g I » the space a body must descend to ac- 
quire the velocity v of the shot or the space due 
to the velocity -v ; consequently the double of 
this, or — — = 
% 
is the greatest horizontal 
range with the velocity v, or at an elevation oi 
45 degrees ; which is nearly half the square of a 
quarter of the velocity. 
In other elevations, the horizontal range is as 
the sine of double the angle of elevation ; so 
that, any other elevation being e, it will be, as 
radius I . sin. 2e - : — x sin. 2e, the 
range at the elevation e, with the velocity v. 
But in a resisting medium, like the atmo- 
sphere, the actual ranges fall far short of the 
above theorems, insomuch that with the great 
velocities the actual or real ranges may be 
less than the tenth part of the potential ranges ; 
so that some balls, which actually range but 
a mile or two, would in vacuo range 20 or 
30 miles. And hence also it happens that 
the elevation of the piece, to shoot farthest in 
the resisting medium, is always below 45°, 
and gradually the more below it as the velo- 
city is greater ; so that the greater velocities 
with which balls are discharged from cannon 
with gunpowder, require an elevation of the 
gun equal to but about 30°, or even less. And 
the less the size of the balls is too, the less 
must this angle of elevation be to shoot the 
farthest with a given velocity. See Projec- 
tile and Gunnery. 
HORN, cornu, in physiology, a hard sub- 
stance growing on the heads of animals, par- 
ticularly the doven-footed quadrupeds; and 
serving them both as weapons of offence and 
defence. 
Horns are not very hard, as they may be 
easily cut with a knife or rasped with a file; 
but they are so tough as not to be capable of 
being pounded in a mortar. When in thin 
plates, they have a degree of transparency, 
and have been sometimes substituted for glass 
in windows. When heated sufficiently, they 
become very soft and flexible, so that their 
shape may be altered considerably. Hence 
they may be gradually squeezed into a mould, 
and wrought into various forms, as is well 
known. 
The quantity of earthy matter which they 
contain is exceedingly small. Mr. Hatchett 
burnt 500 grains of ox-horn. The residuum 
was only 1.5 grain, and not the half of this 
was phosphat of lime. Seventy-eight grains 
of the horn of the chamois left only 0.5 of 
residue, of which less than the half was phos- 
phat of lime. They consist chiefly of a mem- 
branous substance, which possesses the pro- 
perties of coagulated albumen; and probably 
they contain also a little gelatine. Hence 
we see the reason of the products tliat are 
obtained when these substances are subjected 
to distillation. 
r I he horns of the hart and buck must, how- 
ever, be excepted. From the experiments 
ol Scheele and Rouelle, together with those 
of Hatchett, we know that these substances 
possess exactly the properties of bone, and 
are composed of the same constituents, ex- 
cepting only that the proportion of cartilage 
is greater. They are intermediate, then, be- 
tween bone and horn. 
The nails, which cover the extremities of 
the fingers, are attached to the epidermis, 
and come off along with it. Mr. Hatchett 
has ascertained that they are composed chief- 
ly of a membranous substance, which pos- 
sesses the power of coagulated albumen. 
They seem to contain also a little phosphat 
of lime. Water softens, but does not dis- 
solve them. But they are readily dissolved 
and decomposed by concentrated acids and 
alkalies. Hence it appears that nails agree 
with horns in their nature and composition. 
Under the head of nails must be compre- 
hended the talons and claws of the inferior 
animals, and likewise their hoofs, which differ 
in no respect from horn. 
The substance called tortoise-shell is very 
different from shells in its composition, and 
approaches much nearer to the nature of nail : 
for that reason we have placed it here. When 
long macerated in nitric acid, it softens, and 
appears to be composed of membranes laid 
over each other, and possessing the proper- 
ties of coagulated albumen. When burnt, 
500 grains of it yield three of earthy matter, 
consisting of phosphat of lime and soda, with 
a little iron. 
The scales of animals are of two kinds : 
some, as those of serpents and other amphi- 
bious animals, have a striking resemblance to 
horn ; while those of fish bear a greater re- 
semblance to mother-of-pearl. The compo- 
sition of these two kinds of shells is very dif- 
ferent. 
The scales of fish, as has been observed 
by Lewenhoeck, are composed of different 
membranous lamina;. When immersed for 
four or five hours in irttric acid, they become 
transparent, and perfectly membranaceous. 
The acid, when saturated with ammonia, 
gives a copious precipitate of phosphate of 
lime. Hence they are composed of alter- 
nate layers of membrane and phosphat of 
lime. To this structure they owe their bril- 
liancy. Mr. Hatchett found the spicula of 
the shark’s skin to be similar in its composi- 
tion, but the skin itself yielded no phosphat 
of lime. 
The horny scales of serpents, on the other 
hand, are composed alone of a horny mem- 
brane, and are destitute of phosphat of lime. 
They yield, when boiled, but slight traces of 
gelatine: the horn-like crusts which cover 
certain insects and other animals appear from 
Mr. Hatchett’s experiments to be nearly si- 
milar in their composition and nature. 
The casting of the horns of deer is a singu- 
lar phamomenon, the true reason of which 
seems to be a stoppage of the circulation ; so 
that being deprived of the nourishing juice, 
they fall off much in the same manner as the 
leaves of trees in autumn. About ten days 
after the horns are cast, the new ones begin 
to appear : these at first are soft and hairy, 
but they afterwards grow hard, and the crea- 
ture rubs off the hair. 
Horns make a considerable article in the 
arts and manufactures. Bullocks’ horns, soft- 
ened by the lire, serve to make lanthorns, 
combs, knives, ink-horns, tobacco-boxes, &c. 
Dyeing of horns. Black is performed by 
steeping brass in aqua-fortis till it is turned 
green: with this the Tiorn is to be washed 
once or twice, and then put into a warmed 
decoction of logwood and water. Green is 
begun by boiling it, &c. in alum-water, then 
with verdigris, ammoniac, and white-wine 
vinegar, keeping it hot therein till sufficiently 
green. Red is begun by boiling it in alum- 
water, and finished by decoction in a liquor 
compounded of quicklime steeped in rain- 
water, strained, and to every pint an ounce 
of Brazil wood added. In this decoction the 
bone, & c. is to be boiled till sufficiently red. 
Dr. Lewis informs us, that horns receive a 
deep black stain from solution of silver. It 
ought to be diluted to such a degree as not 
sensibly to corrode the subject, and applied 
two or three times, if necessary, at consider- 
able intervals, the matter being exposed as 
much as possible to the sun, to hasten the 
appearance and deepening of the colour. 
Dyeing or staining horn to imitate tor- 
toise-shell. The horn to be dyed mint be 
first pressed into proper plates, scales, or 
other flat form, and the following mixture 
prepared : Take of quick-lime two parts, and 
