What hides this stereogram?

Stereogram - 3D Image

#brainteasers #stereogram #3Dimage

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She criticized my apartment...

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Photophone

In 1882, the photophone was demonstrated by Alexander Graham Bell and Charles Sumner Tainter. In their device, a mirrored silver disc was made to vibrate by speech from a speaking tube. Light reflected off the disc was focused by a parabolic dish onto a selenium photocell. The variations in the reflected light were converted into electrical signals carried to headphones.

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