It seems to be strange to you there is a blind spot on the eyes,Here is an interesting experiment that can make something disappear,when one eye is open. Make a card about the size of a postcard and write two English letters L and R on it,L on the left and R on the right.First,hold the card about 80 cm away and you see both the letters.Then close your right eye and look at the letter R only with your left eye.And now,as you move the card slowly towards you,you'll find the letter L disappearing.But if you move the card nearer to your face,the letter will be seen again.Now do the same experiment with your left eye closed,you'll find the letter R disappearing. Why does the letter disappear? It is because there is a blind spot on the eye.When the image of the letter falls on the blind spot,it won't be seen.That is why either of the letters disappears. .The passage mainly tells us  _  .
how to find the blind spot an interesting experiment where the blind spot is there is a blind spot on the eyes.