Friends who have studied physics should all know.
The refractive index of visible light varies in different environnts, such as glass, air, water, and so on.
These things have a unified term in concept, which is dium.
Nowadays, with optical theoretical research gradually becoming standardized, many middle school students have also understood a principle:
Light can propagate in a dium, but the propagation of light itself does not require a dium.
But don’t forget, Little Niu is in 1665, a period when optical research was still in its infancy.
Therefore, the fact that Little Niu could, just based on a few words from Xu Yun, quickly think of the possibility that seven-colored light might have different effects in different dia in less than half a minute, is entirely an outstanding achievent.
Indeed.
Currently, Little Niu does not yet know that light itself is a boson, which does not need any fermions to propagate—at that ti, the pinnacle theory of optics regarding refraction was a mathematical equivalence derived by Snell, and it was unknown until after his death.
It wasn’t until 1678, when Hewgins and others examined his manuscript, that it was publicly known as the famous Snell’s Law.
Prior to that, it was only derived in an equivalent form by Descartes in "Dioptrique."
And this is a fuzzy account with no clear truth, leading to them still sharing the honor of discovering the law of refraction of light.
Therefore, even though Little Niu’s expression subconsciously included the speculation that visible light couldn’t pass through a certain ’environnt,’ it’s entirely understandable—honestly, to even think of the previous layer is already impressive, right?
Then, looking at the small cluster of colorful light on the ground, Little Niu suddenly thought of sothing again.
He pondered for a few seconds and then asked Xu Yun:
"Fat Fish, since sunlight can be dispersed into seven beams of colored light, are these seven-colored beams different lights?
Also, theoretically, these seven beams of light can be recombined into a beam of white light, right?"
Xu Yun twitched the corner of his mouth; well, he just brought up two more critical points.
Nonetheless, by this ti, he had gradually adapted to this founding master’s abnormal thinking ability, so he quickly adjusted his mindset and said:
"Sorry, Mr. Newton, I only know the answer to the latter question—under the right conditions, the colorful light can be recombined into a beam of white light."
Little Niu was already interested at this point, his eyes glancing around:
"Fat Fish, you ntioned that prisms can also verify the dispersion phenonon?"
"That’s right, and the prism’s effect is much better than lenses."
"Then let’s do it once more with a prism!"
Little Niu quickly looked around and decisively said:
"I’ll go inside to find a prism; I brought back quite a few of these from London before.
You just move the table—the tea table inside will do, just bring it here."
Xu Yun nodded:
"Understood."
Over ten minutes later.
A table about a ter in diater, several prisms, and a black wooden board were placed next to the water tank.
Then Xu Yun stood up a prism, skillfully adjusted the angle, and gave Little Niu an OK sign.
A mont later.
A strip of spectrum appeared on the paperboard behind the prism, and it was noticeably clearer than before.
Seeing this, Xu Yun stepped aside, deliberately not making any indication, curious to see what this youthful founding master could achieve without any hints.
Little Niu ca to the table, bent down and closely examined the spectrum.
He hesitated for a few seconds, picked up a black paperboard.
Cut a circle on it and placed it on the outside of the prism, where the light source was coming from.
A vast amount of sunlight was blocked by this paperboard, with only a beam of circular light passing through the small hole, then...
It still ford a strip of spectrum.
Seeing this situation, Little Niu uttered a soft "hmm."
Perhaps because he wanted to confide in soone, he suddenly looked at Xu Yun again:
"Fat Fish, have you heard of Mr. Descartes’ theory?"
Xu Yun nodded and said:
"Of course I’ve heard of it; I even visited the University of Poitiers once.
Mr. Descartes believes that the color of light cos from the dium between the luminous body and the human eye, and is unrelated to the light source.
The color of light is not a feature inherent to the light, and he also proposed the theory of transformations of light traces."
"You’re right, but see here."
Little Niu held the paperboard in one hand and pointed to the projected strip of spectrum with the other:
"According to Mr. Snell’s equivalence and Mr. Descartes’ theory, the circular light beam should form a circular or elliptical spot after passing through the prism.
Yet after dispersion, the colorful light forms a strip spectrum...
Could it be...
that Mr. Descartes’ theory is flawed?"
After speaking, Little Niu thought for a mont and, before Xu Yun could reply, picked up the paperboard and scissors again, and made an even smaller hole.
He placed this paperboard behind the first prism, using this circular hole to capture any light beam from the colorful light band. (Little Niu once hand-drew this apparatus, (DOI)10.1098/rsta.2014.0213, personally authored by Little Niu, those interested can take a look, truly a soulful artist).
Then Little Niu beckoned Xu Yun, signaling him to co forward:
"Fat Fish, I’ll report data, and you record."
Xu Yun’s pupils shrank slightly, knowing that Little Niu was gradually advancing toward his ultimate "goal," but his expression remained unchanged:
"Okay, Mr. Newton."
Then the two started calculating angles, one holding paper and pen, the other taking asurents.
"Red light, incidence angle i60°, refractive angle β32.2°....."
"Orange light, incidence angle i60°, refractive angle β37.4°....."
"Incidence angle i60°, refractive angle β38.7°....."
Twenty minutes later, four sets, 28 data points recorded.
The refractive index of different types of light in optical glass is different; the deeper reason involves relative perability μr and relative permittivity εr, these two constants need Maxwell’s Equations in diums to calculate, thereafter establishing an intuitive matter and light interaction model, inducting motion equations through linear dissipation force, then solving his steady state using complex numbers, etc...
However, considering it’s not convenient yet to PUA readers....ahem, the content is too complex, everyone only needs to understand the relevant conclusions just from a macro perspective.
After all, Little Niu’s era didn’t have Maxwell’s Equations, did it?
"Purple Light 1.532.... Blue 1.528.... Green 1.519..... Yellow 1.517..... Orange 1.514.... Red 1.513..."
Looking at the fixed sets of data in front of him, Little Niu couldn’t help but take a deep breath.
Clearly.
The refractive indices of different colored lights differ and remain constant, these seven-colored lights have different properties.
Hence, one can derive a conclusion:
White light is indeed not a pure light; it’s composed of different lights.
And this implies...
He might be one step closer to understanding the truth of the world.
anwhile.
Little Niu was gazing at the light divided into seven, and also seven rged into one, suddenly thinking of sothing.
He saw his chest rise and fall a few tis, swiftly running back into the house.
.....
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