Dark room box and liquid-propellant rocket engine: what they have in common

1. Step 1. Dark room box — is part of — Camera obscura. A darkened room or box.
2. Step 2. Camera obscura — evolved into — Camera. A camera is a camera obscura with a light-sensitive layer.
3. Step 3. Camera — is part of — Bubble chamber. Photographing the tracks.
4. Step 4. Bubble chamber — is made of — Hydrogen. The working medium is superheated liquid hydrogen.
5. Step 5. Hydrogen — is used in — Liquid-propellant rocket engine. Hydrogen is an efficient fuel.

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