MON 
MON 
at fop by a horizontal edge : the other point 
of termination, which in the common mono- 
chords, as well as in many musical instru- 
ments, and in the Stanhope monochord, is a 
bridge over which the string is stretched, is 
in this construction effected by two steel 
edges vertically placed, that are capable of 
approaching, or of receding from, one ano- 
ther, like the cheeks of a vice : these being 
fixed on a frame worked by micrometer 
screws, can be easily moved in the vertical 
direction, so as to alter the length of the 
string in any desired proportion: these 
edges are separated occasionally by a spring, 
in order to let the string pass freely through, 
when its length is altered, and are closed 
again, so as to press the string slightly when 
that length is properly adjusted. By means 
of this construction the alteration of the 
tending force, by the application of bridges, 
&c. is wholly avoided. The scale placed 
under the string of this monochord is divid- 
ed into 1(10 equal parts, and each of these 
by a micrometer screw into 1000 equal 
parts j so that, by the aid of a microscope 
and a pi-opcr index, the length of a given 
part of the string may be adjusted on the 
monochord true to the ^jjgdth part of its 
whole length. 
MONOCULUS, in natural history, a 
genus of insects of the order Aptei a. Legs 
four to eight, formed for swimming, and 
very long ; body covered with a crest, or 
shcll,’divided into segments ; antennae some- 
times four, sometimes two, and sometimes 
without any; four feelers, in continual mo- 
tion when swimming, the hind ones very 
small, and hook-shaped. There are about 
60 species, separated into sections. A. With 
a single eye, and crustaceous body. B. 
With a single eye, and bivalve shell ; an- 
tenna; branched. C. With a single eye, 
and bivalve shell ; antennae simple. D. With 
a single eye, and bivalve shell ; antennae 
tufted at the tip. E. With a single eye, 
and univalve shell ; antennae two. F. Shell 
univalve ; two eyes placed beneath. G. 
Shell bivalve; eyes two, placed on the 
back. The greater part of the Monociili 
are very small water insects, requiring the 
assistance of the microscope for the inves- 
tigation of their pai ticidar organs. To this 
there is, however, an exception in the M. 
polyphemus, which inhabits India. This is 
distinguished by tbe title of the Molucco 
crab, or king crab, and grows sometimes to 
the length of four feet. In this species the 
eyes, instead of being approximated, as is 
required in the Linu»an generic character, 
are extremely distant from each other, bc« 
ing situated towards the sides of the shell. 
“ The whole structure of this animal is very 
remarkable, and particularly his eyes, which 
are between the fourth and last pair of 
claws on each side, reckoning from his 
mouth, and excluding the small pair there 
placed, are inserted the rudiments of ano- 
ther pair, or a claw broken off on each side 
at the second joint or elbow; on these ex- 
tremities are the eyes like those of the horns 
of snails ; but under tlie covert of a thick 
and opaque shell nature in that place has 
wonderfully contrived a transparent lantern, 
through which the light is conveyed.” 
MONODON, the narwhal, in natural 
history, a genus of Mammalia, of the order 
Cete. Generic character: tooth (some- 
times two teeth) in the upper jaw, project- 
ing strait forwards, long and spiral ; spiracle 
on the head. The only species of this genus 
is M. monoceros, or the unicorn narwhal ; 
this is found in the northern seas, and ge- 
nerally of the length of twenty feet from 
the mouth to the tail; from a socket in 
the upper jaw on one side, a tooth some- 
what resembling a horn grows, in a perfectly 
straight direction, and a wreathed or screw- 
like foi-m, to the length of six, and occa- 
sionally nine or ten feet, of a li|ht yellow 
colour, and terminating in a sharp point, a 
circumstance by which it is discriminated 
from every other species of whales. The 
incipient protrusion of a second tooth on 
the other side of the jaw is generally per- 
ceivable, and in some instances, though 
rarely, both advance to maturity. The 
narwhals subsist principally upon flat 
fish. 
They are seldom observed in the open 
sea, and frequent the unfrozen spots near 
the coasts of the arctic regions, where they 
seldom fail of their favourite food, and re- 
sort in considerable numbers for the advan- 
tage both of certain supplies and convenient 
respiration. They are taken by the Green- 
landers in great abundance by the harpoon ; 
their flesh is eaten prepared in various ways, 
and the oil and intestines are also articles 
in great request at the table of these unfas- 
tidious people. The tendons are split into 
thin fibres, serving the purposes of thread, 
and the teeth are used sometimes for hunt- 
ing horns, and more frequently as pillars 
and gate-posts in houses. These horns were 
formerly considered as indicative of royal 
state and magnificence, being employed as 
the ornaments of palaces, of which some 
traces are yet in existence. Medical virtue 
