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in English
Mr. HOOKE'S considerations upon Mr. NEWTON'S discourse on light and co
lours were read. Mr. Hooke was thanked for the pains taken in bringing in
such ingenious reflections; and it was ordered, that this paper should be registred33 Register, vol. iv. p. 148.
and a copy of it immediately sent to Mr. NEWTON: and that in the mean time
the printing of Mr. NEWTON'S discourse by itself might go on, and if he did not con
tradict it; and that Mr. HOOKE'S paper might be printed afterwards, it not be
ing thought fit to print them together, lest Mr. NEWTON should look upon it
as a disrespect, in printing so sudden a refutation of a discourse of his, which had
met with so much applause at the Society but a few days before.
Mr. HOOKE'S paper was as follows:
"I have perused the discourse of Mr. NEWTON about colours and refractions,
and I was not a little pleased with the niceness and curiosity of his observations.
But, tho' I wholly agree with him as to the truth of those he hath alledged,
thesis of solving the phenomæna of colours thereby, I confess, I cannot see yet
any undeniable argument to convince me of the certainty threof. For all
the experiments and observations I have hitherto made, nay, and even those
very experiments, which he alledgeth, do seem to me to prove, that white
is nothing but a pulse or motion, propagated through an homogeneous, uni
form and transparent medium: and that colour is nothing but the disturb
ance of that light, by the communication of that pulse to other transparent me
diums, that is, by the refraction thereof: that whiteness and blackness are no
thing but the plenty or scarcity of the undisturbed rays of light: and that
the two colours (than the which there are not more uncompounded in nature)
are nothing but the effects of a compounded pulse, or disturbed propagation
of motion caused by refraction.
But, how certain soever I think myself of my hypothesis (which I did not take
up without first trying some hundreds of experiments) yet I should be very glad
to meet with one experimentum crucis from Mr. NEWTON, that should divorce me
from it. But it is not that, which he so calls, will do the turn; for the same phæ
nomenom will be solved by my hypothesis, as well as by his, without any man
ner of difficulty or straining: nay, I will undertake to shew another hypothesis, differing from both his and mine, that shall do the same thing.
That the ray of light is as it were split or rarified by refraction, is most cer
tain; and that thereby a differing pulse is propagated, both on those sides, and
in all the middle parts of the ray, is easy to be conceived: and also, that differ
ing pulses or compound motions should make differing impressions on the eye,
brain, or sense, is also easy to be conceived: and that, whatever refracting me
dium does again reduce it to its primitive simple motion by destroying the ad
ventitious, does likewise restore it to its primitive whiteness and simplicity.
But why there is a neccessity, that all those motions, or whatever else it be
that makes colours, should be originally in the simple rays of light, I do not
yet understand the necessity of, no more than that all those sounds must be in
the air of the bellows, which are afterwards heard to issue from the organ-
pipes; or in the string, which are afterwards, by different stoppings and strik
ings produced; which string (by the way) is a pretty representation of the shape
of a refracted ray to the eye; and the manner of it may be somewhat imagined
by the similitude thereof: for the ray is like the string, strained between the
luminous object and the eye, and the stop or fingers is like the refracting sur
face, on the one side of which the string hath no motion, on the other a vi
brating one. Now we may say indeed and imagine, that the rest or streight
ness of the string is caused by the cessation of motions, or coalition of all vi
brations; and that all the vibrations are dormant in it: but yet it seems more
natural to me to imagine it the other way.
And I am a little troubled, that this supposition should make Mr. NEWTON
wholly lay aside the thoughts of improving telescopes and microscopes by re
fractions; since it is not improbable, but that he, that hath made so very good an
improvement of telescopes by his own trials upon reflection, would, if he had
prosecuted it, have done more by refraction. And that reflection is not the
only way of improving telescopes, I may possibly hereafter shew some proof
of. The truth is, the difficulty of removing that inconvenience of the split
ting of the ray, and consequently of the effect of colours, is very great; but
yet not insuperable. I have made many trials, both for telescopes and mi
croscopes by reflection, which I have mentioned in my Micrographia, but de
serted it as to telescopes, when I considered, that the focus of the spherical con
cave is not a point but a line, and that the rays are less true reflected to a
point by a concave, than refracted by a convex; which made me seek that by
refraction, which I found could not rationally be expected by reflection: nor
indeed could I find any effect of it by one of six foot radius, which, about se
ven or eight years since, Mr. REEVE made for Mr. GREGORY, with which I
made several trials; but it now appears it was for want of a good encheiria
(from which cause many good experiments have been lost) both which consi
derations discouraged me from attempting further that way; especially since I
found the parabola much more difficult to describe, than the hyperbola or el
lipsis. And I was wholly taken from the thoughts of it, by lighting on divers
ways, which in theory answered all I could wish for; tho' having much more
business, I could not attend to bring them into use for telescopes; tho' for mi
croscopes I have a good while used it. Thus much as to the preamble; I
shall now consider the propositions themselves.
First then, Mr. NEWTON alledgeth, that as rays of light differ in re
frangibility, so they differ in their disposition to exibit this or that colour:
with which I do in the main agree; that is, that the ray by refraction is, as it
were, split or rarified, and that the one side, namely that which is most refracted,
gives a blue, and that which is least a red: the intermediate are the dilutings
and intermixtures of those two, which I thus explain. The motion of light in
an uniform medium, in which it is generated, is propagated by simple and
uniform pulses or waves, which are at right angles with the line of direction;
but falling obliquely on the refracting meduim, it receives another impression
or motion, which disturbs the former motion, somewhat like the vibration of a
string: and that, which was before a line, now becomes a triangular superfi
cies, in which the pulse is not propagated at right angles with its line of direc
tion, but ascew, as I have more at large explained in my Micrographia; and
that, which makes excursions on the one side, impresses a compound motion on
the bottom of the eye, of which we have the imagination of red; and that,
which makes excursions on the other, causes a sensation, which we imagine a blue; and so of all the intermediate dilutings of those colours. Now, that the
intermediate are nothing but the dilutings of those two primary, I hope I have
sufficiently proved by the experiment of the two wedge-like boxes, described
in my Micrographia. Upon this account I cannot assent to the latter part of
tions, or reflections of natural bodies, but original and connate properties, &c.
The second proposition I wholly allow, not exactly in the sense there meant,
but with my manner of expressing it; that is, that part of the split ray, which is
most bent, exhibits a blue, that which is least, a red, and the middle parts midling
colours; and that those parts will always exhibit those colours till the com
pound motions are destroyed, and reduced by other motions to one simple and
uniform pulse as it was at first.
And this will easily explain and give a reason of the phænomena of the third
proposition, to which I do readily assent in all cases, except where the split ray
is made by another refraction, to become intire and uniform, again to diverge
and separate, which explains his fourth proposition.
But as to the fifth, that there are an indefinite variety of primary or original
colours, amongst which are yellow, green, violet, purple, orange, &c. and
an infinite number of intermediate gradations, I cannot assent thereunto, as
suppposing it wholly useless to multiply entities without necessity, since I have
elsewhere shewn, that all the varieties of colours in the world may be made
of two. I agree in the sixth, but cannot approve of his way of explicating
the seventh. How the split ray being made doth produce a clear and uniform
light, I have before shewed; that is, by being united thereby from a superfi
cial motion, which is susceptible of two, to a lineary, which is susceptible of
one only motion; and it is as easy to conceive how all those motions again ap
pear after the rays are again split or rarified. He, that shall but a little consider
the undulations on the surface of a small river of water, in a gutter, or the
like, will easily see the whole manner curiously exemplified.
The eighth proposition I cannot at all assent to, for the reasons above; and
the reasons of the blue flame of brimstone, of the yellow of a candle, the
green of copper, and the various colours of the stars, and other luminous bo
dies, I take to proceed from quite another cause, easily explained by my for
mer hypothesis.
I agree with the observations of the ninth, tenth, and eleventh, though not
with his theory, as finding it not absolutely necessary, being as easily and na
turally explained and solved by my hypothesis.
The reason of the phænomena of my experiment, which he alledgeth, is
as easily solvable by my hypothesis as by his; as are also those, which are men
tioned in the thirteenth. I do not therefore see any absolute necessity to be
lieve his theory demonstrated, since I can assure Mr. NEWTON, I cannot only
solve all the phænomena of light and colours by the hypoythesis I have for
merly printed, and now explicate them by, but by two or three other very dif
course.
Nor would I be understood to have said all this against his theory, as it is
an hypothesis; for I do most readily agree with them in every part thereof, and
esteem it very subtil and ingenious, and capable of solving all the phænomena
of colours: but I cannot think it to be the only hypothesis, nor so certain as
mathematical demonstrations.
But grant his first proposition, that light is a body, and that as many co
lours as degrees thereof as there may be, so many sorts of bodies there may
be, all which compounded together would make white; and grant further,
that all luminous bodies are compounded of such substances condensed, and
that whilst they shine, they do continually send out an indefinite quantity there
of, every way in orbem, which in a moment of time doth disperse itself to the
utmost and most indefinite bounds of the universe; granting these, I say, I
do suppose there will be no great difficulty to demonstrate all the rest of his
curious theory: though yet, methinks, all the coloured bodies in the world
compounded together should not make a white body, and I should be glad
to see an experiment of that kind done on the other side. If my supposition
be granted, that light is nothing but a simple and uniform motion, or pulse
of a homogeneous and adopted (that is a transparent) medium, propagated from
the luminous body in orbem, to all imaginable distances in a moment of time,
and that that motion is first begun by some other kind of motion in the lu
minous body; such as by the dissolution of sulphureous bodies by the air, or
by the working of the air, or the several component parts one upon another,
in rotten wood, or putrifying fish, or by an external stroke, as in diamond, su
gar, the sea-water, or two flints or crystal rubbed together; and that this
motion is propagated through all bodies susceptible thereof, but is blended or
mixt with other adventitious motions, generated by the obliquity of the stroke
upon a refracting body; and that, so long as those motions remain distinct in
the same part of the medium or propagated ray, so long they produce the same
effect, but when blended by other motions, they produce other effects: and
supposing, that by a direct contrary motion to the newly impressed, that ad
ventitious one be destroyed and reduced to the first simple motion; I believe
Mr. NEWTON will think it no difficult matter, by my hypothesis, to solve all the
phænomena, not only of the prism, tinged liquors, and solid bodies, but of
the colours of plated bodies, which seem to have the greatest difficulty. It
is true, I can, in my supposition, conceive the white or unifrom motion of
light to be compounded of the compound motions of all the other colours,
as in any one strait and uniform motion may be compounded of thousands of
compound motions, in the same manner as DESCARTES explicates the reason
of the refraction; but I see no necessity of it. If Mr. NEWTON hath any
argument, that he supposes as absolute demonstration of his theory, I should be
my opinion, as well worthy of contemplation, as any thing else in the world."