atdtda: 31 - pg 871

[kelber at mindspring.com]

http://www.livescience.com/technology/061019_invisibility_cloak.html

"Scientists have created a cloaking device that can reroute certain wavelengths of light, forcing them around objects like water flowing around boulders in a stream. To creatures or machines that see only in microwave light, the cloaked object would appear nearly invisible."

Laura

-----Original Message-----
>From: Bekah <Bekah0176 at sbcglobal.net>


>871:37   "Cyprian recited the appropriate formulæ and  became  
>invisible."
>
> From The Invisible Man by H.G. Wells  (1897) - Chapter 19  (the  
>formula for invisibility concerns refraction and light):
>
>"But I went to work -- like a slave. And I had hardly worked and  
>thought about the matter six months before light came through one of  
>the meshes suddenly -- blindingly! I found a general principle of  
>pigments and refraction, -- a formula, a geometrical expression  
>involving four dimensions. Fools, common men, even common  
>mathematicians, do not know anything of what some general expression  
>may mean to the student of molecular physics. In the books -- the  
>books that Tramp has hidden -- there are marvels, miracles! But this  
>was not a method, it was an idea, that might lead to a method by  
>which it would be possible, without changing any other property of  
>matter, -- except, in some instances, colours, -- to lower the  
>refractive index of a substance, solid or liquid, to that of air --  
>so far as all practical purposes are concerned.
>
>
>Phew!" said Kemp. "That's odd! But still I don't see quite -- I can  
>understand that thereby you could spoil a valuable stone, but  
>personal invisibility is a far cry."
>
>"Precisely," said Griffin. "But consider: Visibility depends on the  
>action of the visible bodies on light. Either a body absorbs light,  
>or it reflects or refracts it, or does all these things. If it  
>neither reflects nor refracts nor absorbs light, it cannot of itself  
>be visible. You see an opaque red box, for instance, because the  
>colour absorbs some of the light and reflects the rest, all the red  
>part of the light, to you. If it did not absorb any particular part  
>of the light, but reflected in all, then it would be a shining white  
>box. Silver! A diamond box would neither absorb much of the light nor  
>reflect much from the general surface, but just here and there where  
>the surfaces were favourable the light would be reflected and  
>refracted, so that you would get a brilliant appearance of flashing  
>reflections and translucencies, -- a sort of skeleton of light. A  
>glass box would not be so brilliant, not so clearly visible, as a  
>diamond box, because there would be less refraction and reflection.  
>See that? From certain points of view you would see quite clearly  
>through it. Some kinds of glass would be more visible than others, a  
>box of flint glass would be brighter than a box of ordinary window  
>glass. A box of very thin common glass would be hard to see in a bad  
>light, because it would absorb hardly any light and refract and  
>reflect very little. And if you put a sheet of common white glass in  
>water, still more if you put it in some denser liquid than water, it  
>would vanish almost altogether, because light passing from water to  
>glass is only slightly refracted or reflected or indeed affected in  
>any way. It is almost as invisible as a jet of coal gas or hydrogen  
>is in air. And for precisely the same reason!"
>
>"Yes," said Kemp, "that is pretty plain sailing."
>
>"And here is another fact you will know to be true. If a sheet of  
>glass is smashed, Kemp, and beaten into a powder, it becomes much  
>more visible while it is in the air; it becomes at last an opaque  
>white powder. This is because the powdering multiplies the surfaces  
>of the glass at which refraction and reflection occur. In the sheet  
>of glass there are only two surfaces; in the powder the light is  
>reflected or refracted by each grain it passes through, and very  
>little gets right through the powder. But if the white powdered glass  
>is put into water, it forthwith vanishes. The powdered glass and  
>water have much the same refractive index; that is, the light  
>undergoes very little refraction or reflection in passing from one to  
>the other.
>
>"You make the glass invisible by putting it into a liquid of nearly  
>the same refractive index; a transparent thing becomes invisible if  
>it is put in any medium of almost the same refractive index. And it  
>you will consider only a second, you will see also that the powder of  
>glass might be made to vanish in air, if its refractive index could  
>be made the same as that of air; for then there would be no  
>refraction or reflection as the light passed from glass to air."
>
>"Yes, yes," said Kemp. "But a man's not powdered glass!"
>
>"No," said Griffin. "He's more transparent!"
>
>"Nonsense!"
>
>"That from a doctor! How one forgets! Have you already forgotten your  
>physics, in ten years? Just think of all the things that are  
>transparent and seem not to be so. Paper, for instance, is made up of  
>transparent fibres, and it is white and opaque only for the same  
>reason that a powder of glass is white and opaque. Oil white paper,  
>fill up the interstices between the particles with oil so that there  
>is no longer refraction or reflection except at the surfaces, and it  
>becomes as transparent as glass. And not only paper, but cotton  
>fibre, linen fibre, wool fibre, woody fibre, and bone, Kemp, flesh,  
>Kemp, hair, Kemp, nails and nerves, Kemp, in fact the whole fabric of  
>a man except the red of his blood and the black pigment of hair, are  
>all made up of transparent, colourless tissue. So little suffices to  
>make us visible one to the other. For the most part the fibres of a  
>living creature are no more opaque than water."
>
>http://www.readprint.com/chapter-10225/H-G--Wells
>
>But Cyprian is in Venice thinking these things and waiting for Theign  
>to show up.
>
>Bekah
>