MED 
MED 
k should be given in some mucilaginous 
fluid. 
MEDIETAS lingua, a jury or inquest 
impanelled, whereof the one half consists of 
natives or denizens, the other strangers, 
and is used in pleas, wherein the one party 
is a stranger, the other a denizen. 
MEDIUM, in logic, the mean or middle 
term of a syllogism, being an argument', rea- 
son, or censideration, for which we affirm or 
deny any thing : or, it is the cause why the 
greater extreme is affirmed or denied of the 
less in the conclusion. 
Medium, in arithmetic, or Arithmetical 
Medium, or mean, called in the schools, 
medium rei, that which is equally distant 
from each extreme, or which exceeds the 
lesser extreme as much as it is exceeded by 
the greater, in respect of quantity not of 
proportion : thus 9 is a medium between 6 
and 12. See Proportion. 
Medium, geometrical, called in the schools 
medium personas, is that where the same 
ratio is preserved between the first and 
second, as between the second and third 
terms, or that which exceeds in the same 
ratio, or quota of itself, as it is exceeded : 
thus 6 is a geometrical medium between 
4 and 9. 
Medium, in philosophy, that space or 
region through which a body in motion 
passes to any point; thus aether is supposed 
to be the medium tlffough which the hea- 
venly bodies move ; air, the medium 
wherein bodies move near our earth ; water, 
the medium wherein fishes live and move ; 
and glass is also a medium of light, as it af- 
fords it a free passage. That density or 
consistence in the parts of the medium, 
whereby the motion of bodies in it is re- 
tai'ded, is called the resistance of the me- 
dium, which together with the force of gra- 
vity, is the cause of the cessation of the mo- 
tion of projectiles. 
Medium, subtle or atliereal. Sir Isaac 
Newton makes it probable, that besides 
the particular serial medium, wherein we 
live and breathe, there is another more 
universal one, which he calls an aethereal 
medium, vastly more rare, subtile, elastic, 
and active than air, and by that means, 
freely permeating the pores and interstices 
of all other mediums, an 1 diffusing itself 
through the whole creation ; and by the 
intervention hereof, he thinks it is, that most 
of the great phenomena of nature are 
effected. This medium he seems to have 
recourse to, as the first and most remote 
physical spring, and the ultimate of all na- 
tural causes. By the vibrations of this me- 
dium, he takes heat to be propagated from 
lucid bodies, and the intenseness of heat in- 
creased and preserved in hot bodies, and 
from them communicated to cold ones. By 
this medium, he takes light to be reflected, 
inflected, refracted, and put alternately 
in fits of easy reflection and transmission, 
which effects he elsewhere ascribes to at- 
traction ; so that this medium appears the 
source and cause even of attraction. Again, 
this medium being much rarer within 
the heavenly bodies than in the heavenly 
spaces, and growing denser as it recedes 
further from them, he supposes the cause of 
the gravitation of these bodies towards each 
other, and of the parts towards the bodies. 
Again from the vibrations of this same me- 
dium excited in the bottom of the eye, by 
the rays of light, and thence propagated 
through the capillaments of the optic nerves 
into the sensory, he takes vision to be per- 
formed ; and so hearing from the vibra- 
tions of this or some other medium excited 
in the auditory nerves by the tremors of the 
air, and propagated through the capilla- 
ments of the nerves into the muscles ; and 
thus contracting and dilating them. 
The elastic force of this medium, he 
shews, must be prodigious. Light moves at 
the rate of 95,000,000 miles in about eight 
minutes, yet the vibrations and pulses of 
this medium, to cause the fits of easy 
reflection and easy transmission, must be 
swifter than light, which is 700,000 times 
swifter than sound. The elastic force of 
this medium therefore in proportion to its 
density must be above 490,000,000,000 
times greater than the elastic force of the 
air in proportion to its density ; the velo- 
cities and pulses of the elastic mediums, 
being in a subduplicate ratio of the elastici- 
ties and the rarities of the mediums taken 
together ; and thus may the vibrations of 
this medium be conceived as the cause of 
the elasticity of bodies. 
MEDULLA. See Anatomy. 
MEDUSA, in natural history, a genus of 
the Vermes Mollusca class and order. Body 
gelatinous, orbicular, and generally flat un- 
derneath ; mouth central, beneath. There 
are forty-four species divided into two sec- 
tions, viz. A. body with ciliate ribs. B. 
body smooth. Tlie animals of this genus 
consist of a tender gelatinous mass of dif- 
ferent figure, furnished with arms pro- 
ceeding from the lower surface ; the larger 
species, when touched, cause a slight tingling 
and redness, and are usually denominated 
