Llarch. 15, 1873.1 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
729 
How, tlien, did it fare with the theory of Newton 
when the deductions from it were brought face to face 
with natural phenomena ? To the mind’s eye, Newton’s 
elastic particles present themselves like particles of 
sensible magnitude. The same reasoning applies to both ; 
the same experimental- checks exist for both. Tested by 
■experiment, then, Newton’s theory was found competent 
to explain many facts, and with transcendent ingenuity 
its author sought to make it account for all. He so far 
succeeded that men so celebrated as Laplace and Malus, 
who lived till 1812, and Biot and Brewster, who lived 
till our own time, were found among his disciples. 
Still, even at an early period of the existence of the 
Emission Theory, one or two great names were found 
recording a protest against it; and they furnish another 
.illustration of the law that, in forming theories, the 
- scientific imagination must draw its materials from the 
world of fact and experience. It was known long ago 
that sound is conveyed in waves and pulses through the 
air; and this truth once well-housed in the mind, was 
transformed into a theoretic conception. It was sup¬ 
posed that light, like sound, might also be the product 
of wave-motion. But what, in this case, could be the 
material forming the waves ? For the waves of sound 
we have the air of our atmosphere ; but the stretch of 
imagination which filled all space with a medium trem¬ 
bling with the waves of light was so bold as to shock 
cautious minds. In one of my latest conversations with 
Sir David Bi’ewster he said to me that his chiei objection 
to the undulatory theory of light was that he could not 
think the Creator guilty of so clumsy a contrivance as 
the filling of space with ether in order to produce light. 
This, I may say, is very dangerous ground, and the 
quarrel of science with Sir David, as with many other 
persons, is that they profess to know too much about the 
mind of the Creator. 
This conception of an ether was advocated by the cele¬ 
brated astronomer, Huyghens, and by the celebrated 
mathematician, Euler. They were, however, opposed by 
Newton, whose authority at the time bore them down. 
• Or shall I say it was authority merely ? Not quite so. 
Newton’s preponderance was in some degree due to the 
fact that, though Huyghens and Euler were right in the 
main, they did not possess sufficient data to prove them¬ 
selves right. No human authority, however high can 
maintain itself against the voice of Nature, speaking 
through experiment. But the voice ot Nature may be 
an uncertain voice, through the scantiness ot data. This 
was the case at the period now referred to, and at such a 
period by the authority of Newton all antagonists were 
naturally overborne. 
Still, this great Emission Theory, which held its 
ground so long, resembled one of those circles which, 
according to Emerson, the force of genius periodically 
draws round the operations of the intellect, but which 
are eventually broken through by pressure from behind. 
.In the year 1773 was born, at Milverton, in Somerset¬ 
shire, one of the most remarkable men that England 
ever produced. He was educated for the profession of a 
physician, but was too strong to be tied down to pro¬ 
fessional routine. He devoted himself to the study of 
natural philosophy, and became in all its departments a 
master. He was also a master of letters. Languages, 
ancient and modern, were housed within his brain, and 
to use the words ot his epitaph, “ he first penetrated the 
obscurity which had veiled for ages the hieroglyphics of 
Eaypt.” It fell to the lot of this man to discover facts 
in optics which Newton’s theory was incompetent to ex¬ 
plain, and his mind roamed in search of a sufficient 
theory. He had made himself acquainted with all the 
phenomena of wave-motion ; with all the phenomena of 
. sound; working successfully in this domain as an original 
discoverer. Thus inlormed and disciplined, he was pre¬ 
pared to detect any resemblance which might reveal itself 
between the phenomena of light and those of wave- 
vmotion. Such resemblances he did detect; and spurred 
on by the discovery, he pursued his speculations and his 
experiments, until he finally succeeded in placing on an 
immovable basis the Undulatory Theory of Light. 
The founder of this great theory was Thomas Young, 
Permit me, by a kind of geometrical construction to give 
you a notion of the magnitude of this man. Let Newton 
stand erect in his age, and Young in his. Draw a 
straight line from Newton to Young, which shall form 
a tangent to the heads of both. This line would slope 
downward from Newton to Young, because Newton was 
certainly the taller man of the two. But the slope would 
not be steep, for the difference of stature was not ex¬ 
cessive. The line would form what engineers call a 
gentle gradient from Newton to Young. Place under¬ 
neath this line the biggest man born in the interval 
between both. He would not, in my opinion, reach the 
line ; for if he did he would be taller intellectually than 
Young, and there was, I believe, none taller. But I do . 
not want you to rest on English estimates of Young; 
the German Helmholtz, a kindred genius, thus speaks of 
him : “ His was one of the most profound minds that the 
world has ever seen; but he had the misfortune to be too 
much in advance of his age. He excited the wonder of 
his contemporaries, who, however, were unable to follow 
him to the heights at which his daring intellect was ac¬ 
customed to soar. His most important ideas lay, there¬ 
fore, buried and forgotten in the folios of the Royal 
Society, until a new generation gradually and painfully 
made the same discoveries, and proved the exactness of 
his assertions and the truth of his demonstrations.” 
It is quite true, as Helmholtz says, that Young was 
in advance of his age ; but something is to be added 
which illustrates the responsibility of our public writers. 
For twenty years this man of genius was quenched— 
hidden from the appreciative intellect of his countrymen 
—deemed in fact a dreamer, through the vigorous 
audacity of a writer who had then possession of the public 
ear, and who in The Edinburgh Itevieiv poured ridicule upon 
Young and his speculations. To the celebrated French¬ 
men Fresnel and Arago, he was first indebted for the 
restitution of his rights, for they, especially Fresnel, re¬ 
made independently, as Helmholtz says, and vastly ex¬ 
tended his discoveries. To the students of his works 
Young has long since appeared in his true light, but these 
twenty blank years pushed him from the public mind, 
which became in turn filled with the fame of Young’s 
colleague at the Royal Institution, Davy, and afterwards 
with the fame of Faraday. Carlyle refers to a remark 
of Nevalis, that a man’s self-trust i3 enormously in¬ 
creased the moment he finds that others believe m him. 
If the opposite remark be true—if it be a fact that public 
disbelief weakens a man’s force, there is no calculating 
the amount of damage these twenty years of neglect may- 
have done to Young’s productiveness as an investigator. 
It remains to be stated that his assailant was Mr. Henry 
Brougham, afterward Lord Chancellor of England. 
Our hardest work is now before us. And as I have 
often had occasion to notice that capacity for hard, work 
depends in a great measure in the antecedent winding 
up of the will and determination, I would call upon you 
to gird up your loins for the labours now before us. If 
we succeed in climbing the hill which faces us to-night, 
our future labours will be comparatively light. _ In the 
earliest writings of the ancients we find the notion that 
sound is conveyed by the air. Aristotle gives expression 
to this notion, and the great architect Vitruvius com- 
pares the waves of sound to waves of water. Lut the 
real mechanism of wave-motion was hidden from the 
ancients, and indeed was not made clear until the time 
of Newton. The central difficulty of the subject was to 
distinguish between the motion of the wave itself, and 
the motion of the particles which at any moment consti¬ 
tute the wave. , 
Stand upon the sea-shore and observe the ad\ ancing 
rollers before they are distorted by the fiiction of the 
bottom. Every wave has a back and a front, and if you 
