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THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[March 22, 1873 
Surely there must be some hidden meaning in this little 
distance d , which turns up so constantly ? One can ima¬ 
gine the intense interest with which Newton pondered its 
meaning. Observe the outcome of his thought. He had 
probably endowed his light-particles with poles, but now 
he is forced to introduce the notion of periodic recurrence. 
How was this to be done ? By supposing the light-par¬ 
ticles animated, not only with a motion of translation, but 
also with a motion of rotation. Newton’s astronomical 
knowledge rendered all such conceptions familiar to him. 
The earth has such a motion. In the time occupied in 
passing over a million and a half of miles of its orbit— 
that is, in twenty-four hours—our planet performs a com¬ 
plete rotation, and in the time required to pass over the 
distance d, Newton’s light-particle must be supposed to 
perform a complete rotation. True, the light-particle is 
smaller than the planet, and the distance d, instead of 
being a million and a half of miles, is a little over the 
ninety-thousandth of an inch. But the two conceptions 
are, in point of quality, identical. 
Imagine, then, a particle entering the film of air where 
it possesses this precise thickness. To enter the film its 
attracted end must be presented. Within the film it is 
able to turn once completely round ; at the other side of 
the film its attracted pole will be again presented; it 
will, therefore, enter the glass at the opposite side of the 
film and be lost to the eye. All round the place of con¬ 
tact, wherever the film possesses this precise thickness, 
the light will equally disappear—we shall have a ring of 
darkness. 
And now observe how well this conception falls in with 
the law of proportionality discovered by Newton. When 
the thickness of the film is 2 d, the particle has time to 
perform two complete somersaults within the film ; when 
the thickness is 3 d, three complete somersaults ; when 
10 c?, ten complete somersaults are performed. It is mani¬ 
fest that in each of these cases, on arriving at the second 
surface of the film, the attracted pole of the particle will 
be presented. It will therefore be transmitted, and, be¬ 
cause no light is sent to the eye, we shall have a ring of 
darkness at each of these places. 
The bright rings follow immediately from the same con¬ 
ception. They occur between the dark rings, the thick¬ 
nesses to which they correspond being also intermediate 
between those answering to the dark ones. Take the case 
of the first bright ring. The thickness of its film is J d ; 
m this interval the rotating particle can perform only half 
a rotation. When, therefore, it reaches the second sur¬ 
face of the film, its repelled pole is presented ; it is, there¬ 
fore, driven back and reaches the eye. At all distances 
round the centre corresponding to this thickness the same 
effect is produced, and the consequence is a ring of bright¬ 
ness. The other bright rings are similarly accounted for. 
At the second one, where the thickness is 1J d, a rotation 
and a half is performed ; at the third, two rotations and 
a half; and at each of these places the particles present 
their repelled poles to the surface of the glass. They are 
therefore sent back to the eye, producing the impression 
of brightness. Here, then, we have unravelled the most 
subtle application that Newton ever made of the Emission 
Theory. 
[The phenomena of interference rings, obtained by 
curved glasses pressed together, was vividly shown upon 
the screen, and much enlarged by double reflection. Then 
coloured glasses were interposed, and the number of rings 
apparent very much increased, so that the whole of the 
light circle given by the instrument seemed covered by 
their ripple ; but they were all of one colour, alternating 
only between light and darkness.] 
Thus Newton, by an exceedingly artificial assumption, 
vaulted over the difficulty presented by the colours of thin 
plates. And as further difficulties in process of time 
thickened round the theory, his disciples tried to sustain 
it with an ingenuity worthy of their master. The new 
difficulties were not anticipated by the theory, but were 
met by new assumptions, until at length the Emission 
Theory became w r hat a distinguished writer calls a “ mob 
of hypotheses.” In the presence of the phenomena of 
interference the theory finally broke down, while the 
whole of these phenomena lie as it were latent in the 
theory of undulation. Newton’s “ fits,” for example, are 
immediately translatable into the lengths of the ether- 
waves. 
Numerous other colours are due to interference. Fine 
scratches drawn upon glass or polished metal reflect the 
waves of light from their sides ; and some, being reflected 
from opposite sides of the same furrow, interfere with 
each other and quench each other. But the obliquity of 
reflection which extinguishes the shorter waves does not 
extinguish the longer ones ; hence the phenomena of co¬ 
lour. These are called the colours of striated surfaces. 
They are well illustrated by mother-of-pearl. This shell 
is composed of exceedingly thin layers, which, when cut 
across by the polishing of the shell, expose their edges and 
furnish the necessary small and regular grooves. The 
most conclusive proof that the colours are due to the me¬ 
chanical state of the surface is to be found in the fact 
that, by stamping the shell carefully upon black sealing- 
wax, we transfer the grooves, and produce upon the wax 
the colours. 
SEIZURE OF UNWHOLESOME DRIED FRUIT. 
At the meeting of the City Commissioners of Sewers on 
Tuesday last, Dr. Tidy, the acting medical officer of health 
for the City, reported that during the last few weeks he 
had condemned as unfit for human food, and ordered to 
be destroyed, 1674 barrels of rotten and diseased figs, 
weighing no less than 187,4881b., and 22 barrels of 
currants, and that 490 barrels of figs in addition were 
now. lying at Custom House Quay in a similarly bad 
condition. The fruit was used almost entirely in the 
manufacture of the cheaper kinds of jam and various sorts 
of “sweet stuff,” which were largely consumed by the 
children of the poor. He had every reason to believe that 
the immense quantity already seized was but a moiety of the 
unsound and unwholesome fruit now lying in bonded ware¬ 
houses, and constantly being delivered out, and he urged 
that a frequent supervision of bonded articles of food was 
imperatively necessary. Dried fruits, after being delivered 
at the various warehouses, remained in bond for eighteen 
months or two years, and no inspection was ever made by 
the wharfingers, who did not consider themselves at liberty, 
except with the owners’ consent, to examine the goods. The 
result was that the fruit became completely rotten before 
any notice was taken of it, and after any sale the wharf 
premises were strewn with thousands of maggots. Dr. 
Tidy pointed out how such a condition of things placed in 
jeopardy the whole contents of the warehouses, and showed 
forcibly the delay which arose, in the present state of the 
law, in obtaining the goods for destruction, for, after the 
orders of the sanitary inspector, the medical officer, the 
magistrate, and the Customs authorities had been obtained, 
the wharfingers would not deliver them unless an order 
from the owner was in addition procured. He also ex¬ 
plained the difficulty in obtaining the requisite information 
to enable the sanitary authorities to act, seeing that the 
wharfingers had an interest in concealment, and there was, 
unfortunately, a market even for rotten figs. He suggested 
the necessity, in the interests of the owners and wharfingers 
themselves, and especially of the public, of some periodical 
examination of bonded articles, of giving to the sanitary 
inspectors increased facilities for inspection, and of pro¬ 
viding that the orders of the medical officer and a justice 
should be sufficient authority for the destruction of goods 
unfit for food, and likely to become a common nuisance# 
The report was referred to the sanitary committee, to 
take such steps in the matter, under the advice of the 
solicitor and medical officer, as they might think desirable. 
