every line or quantity is generated, he gave the name of FLUX
IONS, and to the lines or quantities themselves, that of FLUENTS.
A discovery that successively baffled the acutest and strongest
LIFE OF SIR ISAAC NEWTON. 15
intellects : that, variously modified, has proved of incalculable
service in aiding to develope the most abstruse and the highest
ruths in Mathematics and Astronomy : and that was of itself
enough to render any name illustrious in the crowded Annals of
Science.
At this period, the most distinguished philosophers were direct
ing all their energies to the subject of light and the improvement
of the refracting telescope. Newton, having applied himself to
the grinding of "optic glasses of other figures than spherical," ex
perienced the impracticability of executing such lenses ; and con
jectured that their defects, and consequently those of refracting
telescopes, might arise from some other cause than the imperfect
convergency of rays to a single point. He accordingly "procured
a triangular glass prism to try therewith the celebrated phenom
ena of colours." His experiments, entered upon with zeal, and
conducted with that industry, accuracy, and patient thought, for
which he was so remarkable, resulted in the grand conclusion,
that LIGHT WAS NOT HOMOGENEOUS, BUT CONSISTED OF RAYS,
SOME OF WHICH WERE MORE REFRANGIBLE THAN OTHERS. This
profound and beautiful discovery opened up a new era in the
History of Optics. As bearing, however, directly upon the construc
tion of telescopes, he saw that a lens refracting exactly like a prism
would necessarily bring the different rays to different foci, at
different distances from the glass, confusing and rendering the
vision indistinct. Taking for granted that all bodies produced
spectra of ^
jtial length, he dismissed all further consideration of
the refracting instrument, and took up the principle of reflection.
Rays of all colours, he found, were reflected regularly, so that the
angle of reflection was equal to the angle of incidence, and hence
he concluded that ojitical instruments might be brought to any
degree of perfection imaginable, provided reflecting specula of
the requisite figure and finish could be obtained. At this stage
of his optical researches, he was forced to leave Cambridge on
account of the plague which was then desolating England.
He retired to Woolsthorpe. The old manor-house, in which he
was born, was situated in a beautiful little valley, on the west side
of the river Witham ; and here in the quiet home of his boyhood,
2
16 LIFE OF SIR ISAAC NEWTON.
he passed his days in serene contemplation, while the stalking
pestilence was hurrying its tens of thousands into undistinguisha
ble graves.
Towards the close of a pleasant day in the early autumn of
1666, he was seated alone beneath a tree, in his garden, absorbed
in meditation. He was a slight young man ;
in the twenty-fourth
year of his age ; his countenance mild and full of thought. For
a century previous, the science of Astronomy had advanced with
rapid strides. The human mind had risen from the gloom and
bondage of the middle ages, in unparalleled vigour, to unfold the
system, to investigate the phenomena, and to establish the laws
of the heavenly bodies. Copernicus, Tycho Brahe, Kepler,
Galileo, and others had prepared and lighted the way for him
who was ta give to their labour its just value, and to their genius
its true lustre. At his bidding isolated facts were to take order
as parts of one harmonious whole, and sagacious conjectures grow
luminous in the certain splendour of demonstrated truth. And
this ablest man had come was here. His mind, familiar with
the knowledge of past effort, and its unequalled faculties develop
ed in transcendant strength, was now moving on to the very
threshold of Its grandest achievement. Step by step the untrod
den path was measured, till, at length, the entrance seemed dis
closed, and the tireless explorer to stand amid the first opening
wonders of the universe.
The nature of gravity that mysterious power which causes
all bodies to descend towards the centre of the earth had, in
deed, dawned upon him. And reason busily united link to link
of that chain which was yet to be traced joining the least to the
vastest, the most remote to the nearest, in one harmonious bond.
From the bottoms of the deepest caverns to the summits of the
highest mountains, this power suffers no sensible change : may not
its action, then, extend to the moon ? Undoubtedly : and furthei
reflection convinced him that such a power might be .sufficient for
retaining that luminary in her orbit round the earth. But, though
this power suffers no sensible variation, in the little change of
distance from the earth s centre, at which we may place our-
. lves, yet, at the distance of the moon, :miy not its force undergo
LIFE OF SIR ISAAC NEWTON. 17
more or less diminution ? The conjecture appeared most proba
ble : and, in order to estimate what the degree of diminution
might be, he considered that if the moon be retained in her orbit
by the force of gravity, the primary planets must also be carried
round the sun by the like power; and, by comparing the periods
of the several planets with their distances from the sun, he found
that, if they were held in their courses by any power like gravity,
its strength must decrease in the duplicate proportion of the in
crease of distance. In forming this conclusion, he supposed the
planets to move in perfect circles, concentric to the sun. Now
was this the law of the moon s motion ? Was such a force, em
anating from the earth and directed to the moon, sufficient, when
diminished as the square of the distance, to retain her in her
orbit ? To ascertain this master-fact, he compared the space
through which heavy bodies fall, in a second of time, at a given
distance from the centre of the earth, namely, at its surface, with
the space through which the moon falls, as it were, to the earth,
in the same time, while revolving in a circular orbit. He was
absent from books ; and, therefore, adopted, in computing the
earth s diameter, the common estimate of sixty miles to a degree
of latitude as then in use among geographers and navigators.
The result of his calculations did not, ot course, answer his ex
pectations ; hence, he concluded that some other cause, beyond the
reach of observation analogous, perhaps, to the vortices of Des
cartes joined its action to that of the power of gravity upon the
rnooil. Though by no means satisfied, he yet abandoned awhile
further inquiry, and remained totally silent upon the subject.
These rapid marches in the career of discovery, combined with
the youth of Newton, seem to evince a penetration the most
lively, and an invention the most exuberant. But in him there
was a conjunction of influences as extraordinary as fortunate.
Study, unbroken, persevering and profound carried on its inform
ing and disciplining work upon a genius, natively the greatest,
and rendered freest in its movements, and clearest in its vision,
through the untrammelling and enlig} tenirig power of religion.
And, in this happy concurrence, are to be sought the elements of
those amazing abilities, which, grasping, with equal facility, the
18 LIFE OF SIR ISAAC NEWTON.
minute and the stupendous, brought these successively to light,
and caused science to make them her own.
In 1667, Newton was made a Junior Fellow ; and, in the year
following, he took his degree of Master of Arts, and was appoint
ed to a Senior Fellowship.
On his return to Cambridge, in 1668, he resumed his optical
labours. Having thought of a delicate method of polishing metal,
he proceeded to the construction of his newly projected reflect
ing telescope ; a small specimen of which he actually made with
his own hands, It was six inches long ; and magnified about
forty times ;
a power greater than a refracting instrument of six
feet tube could exert with distinctness. Jupiter, with his four
satellites, and the horns, or moon-like phases of Venus were
plainly visible through it. THIS WAS THE FIRST REFLECTING
TELESCOPE EVER EXECUTED AND DIRECTED TO THE HEAVENS.
He gave an account of it, in a letter to a friend, dated February 23d,
1668-9 a letter which is also remarkable for containing the firs
allusion to his discoveries "
concerning the nature of light." En
couraged by the success of his first experiment, he again executed
with his own hands, not long afterward, a second and superior
instrument of the same kind. The existence of this having come
to the knowledge of the Royal Society of London, in 1671, they
requested it of Newton for examination. He accordingly sent it
to them, It excited great admiration; it was shown to the king*
a drawing and description of it was sent to Paris ; and the telescope
itself was carefully preserved in the Library of the Society.
Newton lived to see his invention in public use, and of eminent
service in the cause of science.
In the spring of 1669, he wrote to his friend Francis Aston,
Esq., then about setting out on his travels, a letter of advice and
directions, it was dated May 18th, and is interesting as exhibit
ing some of the prominent features in Newton s character.
Thus :
" Since in your letter you give me so much liberty of spending
my judgment about what may be to your advantage in travelling,
1 shall do it more freely than perhaps otherwise would have been
decent, Fir,c
t, then, I will lay down some general rules, most of
LIFE OF SIR ISAAC NEWTON. 19
which, I bolieA e, you have considered already ; but if any of
them be new to you, they may excuse the rest ;
if none at all,
yet is my punishment more in writing than yours in reading.
"When you come into any fresh company. 1. Observe their
humours. 2. Suit your own carriage thereto, by which insinua
tion you will make their converse more free and open. 3. Let
your discourse be more in queries and doubtings than peremptory
assertions or disputings, it being the design of travellers to learn,
not to teach. Besides, it will persuade your acquaintance that
you have the greater esteem of them, and so make them more
ready to communicate what they know to you ; whereas nothing
sooner occasions disrespect and quarrels than peremptoriness.
You will find little or no advantage in seeming wiser or much
more ignorant than your company. 4. Seldom discommend any
thing though never so bad, or do it but moderately, lest you be
unexpectedly forced to an unhandsome retraction. It is safer to
commend any thing more than it deserves, than to discommend
a thing so much as it deserves; for commendations meet not
so often with oppositions, or, at least, are not usually so ill re
sented by men that think otherwise, as discommendations ; and
you will insinuate into men s favour by nothing sooner than seem
ing to approve and commend what they like
; but beware o
doing it by comparison. 5. If you be affronted, it is better, in c
foreign country, to pass it by in silence, and with a jest, though
with some dishonour, than to endeavour revenge ; for, in the first
case, your credit s ne er the worse when you return into England,
or come into other company that have not heard of the quarrel.
But, in the second case, you may bear the marks of the quarrel
while you live, if you outlive it at all. But, if you find yoursell
unavoidably engaged, tis best, I think, if you can command your
passion and language, to keep them pretty evenly at some certain
moderate pitch, not much heightening them to exasperate your
adversary, or provoke his friends, nor letting them grow overmuch
dejected to make him insult. In a word, if you can keep reason
above passion, that and watchfulness will be your best defendants.
To which purpose you may consider, that, though such excuses
is this He provok t me so much I could not forbear may pass
20 LIFE OF SIR ISAAC NEWTON.
among friends, yet amongst strangers they are insignificant, ina
only argue a traveller s weakness.
" To these I may add some general heads for inquiries or ob
servations, such as at present I can think on. As, 1. To observe
the policies, wealth, and state affairs of nations, so far as a solif
ary traveller may conveniently do. 2. Their impositions upon
all sorts of people, trades, or commodities, that are remarkable.
3. Their laws and customs, how far they differ from ours. 4.
Their trades and arts wherein they excel or come short of us in
England. 5. Such fortifications as you shall meet with, their
fashion, strength, and advantages for defence, and other such mili
tary affairs as are considerable. 6. The power and respect be
longing to their degrees of nobility or magistracy. 7. It will not
be time misspent to make a catalogue of the names and excellen
cies of those men that are most wise, learned, or esteemed in any
nation. 8. Observe the mechanism and manner of guiding ships.
9. Observe the products of Nature in several places, especially in
mines, with the circumstances of mining and of extracting metals
or minerals out of their ore, and of refining them ; and if you
meet with any transmutations out of their own species into
another (as out of iron into copper, out of any metal into quick
silver, out of one salt into another, or into an insipid body, &c.),
those, above all, will be worth your noting, being the most luciferous,
and many times lucriferous experiments, too, in philosophy.
10. The prices of diet and other things. 11. And the staple
commodities of places.
" These generals (such as at present I could think of), if they
will serve for nothing else, yet they may assist you in drawing up
a model to regulate your travels by. As for particulars, these that
follow are all that 1 can now think of, viz.
; whether at Schemnitium,
in Hungary (where there are mines of gold, copper, iron,
vitriol, antimony, &c.). they change iron into copper by dissolving
t in a vitriolate water, which they find in cavities of rocks in the
mines, and then melting the slimy solution in a stroi ig fire, which
in the cooling proves copper. The like is said to be done in other
places, which I cannot now remember ; perhaps, too, it may be
lone in Italy. For about twenty or thirty years agone there was
LIFE OF SIR ISAAC NEWTON, 21
a certain vitriol came from thence (called Roman vitriol), but of
a nobler virtue than that which is now called by that name ;
which vitriol is not now to be gotten, because, perhaps, they make
a greater gain by some such trick as turning iron into copper
with it than by selling it. 2. Whether, in Hungary, Sclavonia,
Bohemia, near the town Eila, or at the mountains of Bohemia
near Silesia, there be rivers whose waters are impregnated with
gold ; perhaps, the gold being dissolved by some corrosive water
like aqua regis, and the solution carried along with the stream,
that runs through the mines. And whether the practice of laying
mercury in the rivers, till it be tinged with gold, and then strain
ing the mercury through leather, that the gold may stay behind,
be a secret yet, or openly practised. 3. There is newly con
trived, in Holland, a mill to grind glasses plane withal, and I
think polishing them too ; perhaps it will be worth the while to see
it. 4. There is in Holland one Borry, who some years since
was imprisoned by the Pope, to have extorted from him secrets
(as I am told) of great worth, both as to medicine and profit, but
he escaped into Holland, where they have granted him a guard.
I think he usually goes clothed in green. Pray inquire what you
can of him, and whether his ingenuity be any profit to the Dutch.
You may inform yourself whether the Dutch have any tricks to
keep their ships from being all worm-eaten in their voyages to
the Indies. Whether pendulum clocks do any service in finding
out the longitude, &c.
" I am very weary, and shall not stay to part with a long
compliment, only I wish you a good journey, and God be with
you."
It was not till the month of June, 1669, that our author made
known his Method of Fluxions. He then communicated the
work which he had composed upon the subject, and entitled,
ANALYSIS PER EQUATIONES NUMERO TERMINORUM INFINITAS,
to his friend Dr. Barrow. The latter, in a letter dated 20th of the
same month, mentioned it to Mr. Collins, and transmitted it to
him, on the 31st of July thereafter. Mr. Collins greatly approv>
ed of the work ; took a copy of it
; and sent the original back
to Dr. Barrow. During the same and the two following years, Mr
< LIFE OF SIR ISAAC NEWTON.
Collins, by his extensive correspondence, spread the knowledge
of this discovery among the mathematicians in England, Scotland,
France, Holland and Italy.
Dr. Barrow, having resolved to devote himself to Theology,
resigned the Lucasian Professorship of Mathematics, in 1669, in
favour of Newton, who accordingly received the appointment to
the vacant chair.
During the years 1669, 1670, and 1671, our author, as such
Professor, delivered a course of Optical Lectures. Though these
contained his principal discoveries relative to the different refrangibility
of light, yet the discoveries themselves did not be
come publicly known, it seems, till he communicated them to the
Royal Society, a few weeks after being elected a member there
of, in the spring of 1671-2. He now rose rapidly in reputation,
and was soon regarded as foremost among the philosophers of the
age. His paper on light excited the deepest interest in the Royal
Society, who manifested an anxious solicitude to secure the author
from the "
arrogations of others," and proposed to publish his
discourse in the monthly numbers in which the Transactions were
given to the world. Newton, gratefully sensible of these expres
sions of esteem, willingly accepted of the proposal for publication.
He gave them also, at this time, the results of some further ex
periments in the decomposition and re-composition of light : that
the same degree of refrangibility always belonged to the same
colour, and the same colour to the same degree of refrangibility :
that the seven different colours of the spectrum were original, or
simple, and that whiteness^ or white light was a compound of all
these seven colours.
The publication of his new doctrines on light soon called forth
violent opposition as to their soundness. Hooke and Huygens
men eminent for ability and learning were the most conspicuous
of the assailants. And though Newton effectually silenced all his
adversaries, yet he felt the triumph of little gain in comparison
.vith the loss his tranquillity had sustained. He subsequently renarked
in allusion to this controversy and to one with whom
he was destined to have a longer and a bitterer conflict " I was
so persecuted with discussions arising from the publication of m v
LIFE OF SIR ISAAC NEWTON. 23
theory ot light, that I blamed my own imprudence for parting
with so substantial a blessing as rny quiet to run after a shadow.7
In a communication to Mr. Oldenburg, Secretary of the Royal
Society, in 1672, our author stated many valuable suggestions re
lative to the construction of REFLECTING MICROSCOPES which he
considered even more capable of improvement than telescopes.
He also contemplated, about the same time, an edition of Kirickhuysen
s Algebra, with notes and additions; partially arranging,
as an introduction to the work, a treatise, entitled, A Method of
Fluxions ; but he finally abandoned the design. This treatise,
however, he resolved, or rather consented, at a late period of his
life, to put forth separately ; and the plan would probably have
been carried into execution had riot his death intervened. It was
translated into English, and published in 1736 by John Colson,
Professor of Mathematics in Cambridge.
Newton, it is thought, made his discoveries concerning the
INFLECTION and DIFFRACTION of light before 1674. The phe
nomena of the inflection of light had been first discovered more
than ten years before by Grimaldi. And Newton began by re
peating one of the experiments of the learned Jesuit admitting
a beam of the sun s light through a small pin hole into a dark
chamber : the light diverged from the aperture in the form of a,
cone, and the shadows of all bodies placed in this light were
larger than might have been expected, and surrounded with three
coloured fringes, the nearest being widest, and the most remote
the narrowest. Newton, advancing upon this experiment, took
exact measures of the diameter of the shadow of a human hair,
and of the breadth of the fringes, at different distances behind it,
and discovered that these diameters and breadths were not pro
portional to the distances at which they were measured. He
hence supposed that the rays which passed by the edge of the
hair were deflected or turned aside from it, as if by a repulsive
force, the nearest rays suffering the greatest, the more remote a
less degree of deflection. In explanation of the coloured fringes,
he queried : whether the rays which differ in refrangibility do not
differ also in flexibility, and whether they are n<t, by these dif
ferent inflections, separated from one another, so as after separa
< LIFE OF SIR ISAAC NEWTON.
tion to make the colours in the three fringes above described ?
Also, whether the rays, in passing by the edges and sides ol
bodies, are not bent several times backwards and forwards with
an eel-like motion the three fringes arising from three such
bendings ? His inquiries on this subject were here interrupted
and fiever renewed.
His Theory of the COLOURS of NATURAL BODIES was commu
nicated to the Royal Society, in February, 1675. This is justly
regarded as one of the profoundest of his speculations. The fun
damental principles of the Theory in brief, are : That bodies
possessing the greatest refractive powers reflect the greatest
quantity of light ; and that, at the confines of equally refracting
media, there is no reflection. That the minutest particles of al
most all natural bodies are in some degree transparent. That
between the particles of bodies there are pores, or spaces, either
empty or filled with media of a less density than the particles
themselves. That these particles, and pores or spaces, have some
definite size. Hence he deduced the Transparency, Opacity, and
colours of natural bodies. Transparency arises from the particles
and their pores being too small to cause reflection at their com
mon surfaces the light all passing through ; Opacity from the
opposite cause of the particles and their pores being sufficiently
large to reflect the light which is "
stopped or stifled
7
by the
multitude of reflections ; and colours from the particles, accord
ing to their several sizes, reflecting rays of one colour and trans
mitting those of another or in other words, the colour that
meets the eye is the colour reflected, while all the other rays are
transmitted or absorbed.
Analogous in origin to the colours of natural bodies, he con
sidered the COLOURS OF THIN PLATES. This subject was interest
