LIGHT. 
it is even suspected, that there are many 
stars whose light has not yet arrived at us 
since tlieir creation. And this, by-the-bye, 
may perhaps sometimes account for the ap- 
pearance of new stars in the heavens. Our 
excellent astronomer. Dr. Bradley, after- 
wards found nearly the same velocity of 
light as Roemer, from his accurate observa- 
tions, and most ingenious theory, to ac- 
count for some apparent motions in the fix- 
ed stars ; for an account of which see Aber- 
ration o/’/igW. By a long series of these 
observations, he found the difference be- 
tween tlie true and apparent place of seve- 
ral fixed stars, for different times of the 
year; which difference could no otherwise 
be accounted for, than for the progressive 
rays of light. From the mean quantity of 
this difference he ingeniously found, that 
the ratio of the velocity of light to the velo- 
city of the earth in its orbit, was as 10,313 
to 1, or that light moves 10,313 times faster 
than the earth moves in its orbit about the 
sun ; and as this latter motion is at the rate 
of 18|i miles per second nearly, it fol- 
lows that the former, or the velocity of 
light, is at the rate of about 195,000 miles 
in a second ; a motion according to which 
it will require just 8' 7'' to move from the 
sun to the earth, or about 95,000,000 of 
miles. 
It was also inferred, from the foregoing 
principles, that liglit proceeds with the same 
velocity from all the stars. And hence it 
follows, if we suppose that all the stars are 
not equally distant from us, as many argu- 
ments prove, that the motion of light, all the 
way it passes through the immense space 
above our atmosphere, is equable or uni- 
form. And since the different methods of 
determining the velocity of light, thus agree 
in the result, it is reasonable to conclude, 
that in the same medium, light is propa- 
gated with the same velocity after it has 
been reflected as before. For an account 
of Mr. Melville's hypothesis of the different 
velocities of differently coloured rays, see 
Colour. 
To the doctrine concerning the mate- 
riality of light, and its amazing velocity, se- 
veral objections have been made, of which 
the most considerable is ; that as rays of 
light are continually passing in different di- 
rections from every visible point, they must 
necessarily interfere with each other in such 
a manner as entirely to confound all dis- 
tinct perception of objects, if not quite to 
destroy the whole sense of seeing ; not to 
mention the continual waste of substance. 
which a constant emission of particles must 
occasion in the luminous body, and there- 
by, since the creation, must have greatly di- 
minished the matter in the sun and stars, as 
well as increased the bulk of tlie earth and 
planets, by the vast quantity of particles of 
light absorbed by them in so long a period 
of time. But it has been replied, that if 
light were not a body, but consisted in 
mere prcssion or pulsion, it could never be 
propagated in right lines, but would be 
continually inflected ad umbram. Thus, Sir 
Isaac Newton : “A pressure on a fluid me- 
dium, i. e. a motion propagated by such a 
medium, beyond any obstacle, winch im- 
pedes any part of its motion, cannot be pro- 
pagated in right lines, but will be always 
inflecting and diffusing itself every way, to 
the quiescent medium beyond that obsta- 
cle. 
The power of gravity tends downw-ards ; 
but the pressure of water arising from it 
tends every way with an equable force, and 
is propagated with equal ease and equal 
strength, in curves as in straight lines. 
Waves, on the surface of the water, gliding 
by the extremes of any very large obstacle, 
inflate and dilate themselves, still diffusing 
gradually into the quiescent water beyond 
that obstacle. The waves, pulses, or vibra- 
tions of the air, wherein sound consists, are 
manifestly inflected, though not so consi- 
derably as the waves of water ; and sounds 
are propagated with equal ease through 
crooked tubes and through straight lines ; 
but light was never known to move in any 
curve, nor to inflect itself ad umbram.” 
It must be acknowledged, however, that 
many philosophers, both English and fo- 
reigners, have recurred to the opinion, that 
light consists of vibrations propagated from 
the luminous body, through a subtle ethe- 
real medium. 
Dr. Franklin, in a letter dated April 23 , 
1752, expresses his dissatisfaction with the 
doctrine, that light consists of particles of 
matter continually driven off from the sun’s 
surface, with so enormous a swiftness. 
“ Must not,” says he, “ the smallest portion 
conceivable have, with such a motion, a 
force exceeding that of a twenty- four 
pounder discharged from a cannon ? Must 
not the sun diminish exceedingly by such a 
waste of matter ; and the planets, instead 
of drawing nearer to him, as some have 
feared, recede to greater distances, through 
the lessened attraction ? yet these particles, 
with this amazing motion, will not drive be- 
fore them, or remove, the least and slight- 
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