Final answer:
The illusion where two lines appear to be different lengths though they are the same is known as the Müller-Lyer illusion.
Step-by-step explanation:
The illusion where two lines appear to be of different lengths even though they are the same is known as the Müller-Lyer illusion.
This is a classic example of a visual illusion where the perception of the line length is distorted by the presence of arrow-like figures at the ends of the lines.
The Müller-Lyer illusion demonstrates that our sensory perception can be faulty, leading to misrepresentation of reality.
When discussing illusions, there is also an important link to the concept of philosophical skepticism, which suggests that knowledge in some areas may be impossible due to the fallibility of our perception.