# The Bourdon Optical Illusion

There’s a new optical illusion in town, and its name is “Bourdon Illusion“. The Bourdon  illusion is the apparent “bentness” of the straight edge of a figure consisting of two elongated triangles arranged apex to apex.

Like you see in the image on your left, the upper side of the left-lower triangle is actually aligned with the upper side of the right-upper triangle, the former appears to tilt counterclockwise while the latter clockwise. What we are seeing here is “seemingly bent” type of illusion. But why?

Further, I’ve added three rather subtle illusions, each showing bent lines. In Bourdon’s illusion, to the left, the straight left hand edge looks bent again. In Humphrey’s figure, (central object), the straight, loose line touching the corner of the cube looks bent. In the figure to the right, the straight line interrupted by the corner looks bent.

I don’t think we really understand any of these illusions, and since they are not very dramatic, you don’t notice them very often. There’s probably a different explanation for each. For example, both the left and middle figures show a bent line that is the backbone of two triangles meeting at a point, so you might think “Hello, we’re getting somewhere”. But then you notice that the lines bend in different directions relative to the triangles inside each illusion.

## 29 Replies to “The Bourdon Optical Illusion”

1. Raninf says:

Awesome.

Yea, but the cube one(to me, at least) only appears bent when I focus on it.

2. pineapple jo says:

i need a bourbon now

3. Spider says:

Whoa, they look bent!

That was sarcasm =D It’s not a very dramatic illusion, I agree, Vurdlak. But I understand that you can’t post explosive great illusion day in day out. So this one is okay. The middle one, Humphrey thingie, is the best one, in my opinion.

Keep up the good work, dude!

4. No one, says:

That is cool and weird at the same time!!!

first post? if so cool!

5. Shannon says:

Old geometry trick.

6. danny says:

Cool .. kinda confusing though :D

7. Thøm says:

As you say, they are not very dramatic

8. maximiwax says:

i don’t get it…the upper parts seem to be a line and the lower parts seem to be a bow or what?
and the other ones look quite normal to me too

maybe i’m just too stupid to really see the sense of these illusion ^^

9. Dave says:

Well, I have to say that all those lines look straight to me. I don’t see any bending…

Strange as I usually see these illusions and love them!!

10. JulianaBlue says:

I can understand as to why most people would see a bent line.

With the way the black triangle “edges” are set up, the majority of people would look at the ‘bottom’ of the triangles, not the ‘top’.

Even I did at first.

But! If you would clearly focus on the ‘top’ of the triangle edges, it does look like a straight line.

Maybe I’m wrong, but it’s just my own guess. :D

That’s very lame. Only the line in he cube look bended.

12. Liam says:

i dont get it

13. Zachary says:

cool! my brother and I think it is cool. can you post some more?

14. what is this?Is this a scary optical illusion?Next time,show some scarier optical illusion!

15. Heather says:

I’m not really seeing any thing “bend” except for the triangles.

16. Detective Kitty says:

…this illusion is rather simple and is just the matter of the mesurements your brain makes…the two lines make up the illusion

17. chris says:

this is awesome

18. Nick says:

Cool And first!!!

19. Bobbie says:

very interesting. i like it!

20. Tim says:

This sucks

1. kaylen murphy says:

give some encouragement

21. Burn On. ~Pyro~ says:

Errr I think these aren’t the best illusions ever. But nice concept! (:

22. Shannon says:

It’s been two or three days now for this illusion and there still aren’t even comments for us to read. I know there are comments because I left one two days ago.

23. Shannon says:

Okay, maybe I commented yesterday instead of two days ago.

24. Grand Dizzy says:

There must be something wrong with me.

All of those lines look absolutely perfectly straight to me, from the moment I saw them.

25. karryssa says:

it looks like there is a wall behind the cube if you look at it carefully.

26. kaylen murphy says:

some of these are whack but some are ok and some are amazing but what do i know cuase i didnt make any