… never mind the bee and pigeons!
Okay time to talk about if an invisible man has to be blind. Yes, it’s reasonable to believe so. For starters, how the heck would light rays impinge on his retina if they were not there -- because that’s what invisible retinas are like. Like they’d left the body and gone for a long walk on a short pier. So they would go right through the total un-visibility of his whole body too including the head where his eyes were supposed to be when he was capable of being seen.
But wait. Here’s the caveat. Think of this now: what if science fiction writer H G Wells was a bee? Yes you heard that right -- a bee; you know the guys who go for honey and things. The name of his book would then have been “The Invisible Bee” except this unseen insect would have still been able to see and not because of multiple lenses in compound eyes but because bees are supposed to be able to see in ultraviolet and infrared light. These radiation don’t impinge on normal (read, human) retinas.
Or take some kinds of migratory pigeons. Some of those critters can seemingly “sense” the Earth’s magnetic field as they contain the mineral magnetite in their heads. This enables them to “see” in which direction they’re headed but in a sense that’s magnetic, not visual. Is that vision, or what? What does seeing really mean? Some electrical impulses from the back of our eyes are transmitted electrochemically which are then interpreted in the visual cortex of the brain to become what we believe is sight. Is that seeing?
The problem submitted by Dr Vinayak Shukla, firstname.lastname@example.org was: “A farmer came to town with some watermelons. He sold half of them plus half a melon. And he found that he had one whole melon left. How many melons did he take to town?”
The farmer had three melons when he went to town. -- Advaithram Ravichandran, email@example.com
He brought three melons. Sold half of them plus half. This means 3/2 + 1/2. That is 2. Hence 1 fruit is remaining. -- firstname.lastname@example.org
(1) I really enjoy your column. My son Arnav too enjoys it. The answer to watermelon riddle is three watermelons. This was solved by my wife Mona. (2) The answer to bear riddle is: the colour of the bear is white. -- Rajeev Chourey, email@example.com
Some time back another problem was: “Applying a balm ointment on the forehead helps in relieving a headache? But how does it do so?”
Pain balms work on the principle of counter irritant. Instead of actually relieving the pain they suppress it by causing irritation at the point where they are applied. They generally contain methyl salicylate, menthol, and camphor which are easily absorbed through the skin. Methyl salicylate acts as a painkiller, camphor produces a cool sensation and acts as a mild local anaesthetic and camphor numbs nerve endings. -- Neethi Balagopal, firstname.lastname@example.org
And finally, the problem was: “Why would an invisible man be blind?” The result is, I’ve been underwhelmed by so many people who know the answer besides me.
This is an easy one. The required condition for a person to be invisible is that the refractive index of his/her body should be equal to the refractive index of air so that light rays will pass through the body. But in this case, the light rays will also pass through his/her eyes without forming any image on them. In short, no refraction = no image formation = blind. -- Sharmistha Tosh, email@example.com
Besides the gracious S T above, here are the next first 10 correct answers: -- Rajaraman V, firstname.lastname@example.org; Radhakanta Pradhan, email@example.com; Sohan Banerjee, firstname.lastname@example.org; Kushal H, email@example.com; M Ranganath Mallya, firstname.lastname@example.org; Krishnanunni Mukundan, email@example.com; YVPHFCK, firstname.lastname@example.org; Krishna D V, email@example.com; Sunil Mohandas, firstname.lastname@example.org; Unnikrishnan P M, email@example.com;
With reference to the answers given to my problem of the dampening effect on steel ball dropped on a plastic sheet I think John Mathew, firstname.lastname@example.org, has reasoned correctly. Especially about plastics’ ability to stretch out and its absorption energy. Shashi Thakur, email@example.com, tells about “rolling resistance” which is only a post impact effect. I thank both for their response though.-- Prabhakar M G, firstname.lastname@example.org
BUT GOOGLE THIS NOW
How do birds stay on their perches or on a branch even when they are asleep, without falling off?
— Sharma is a scriptwriter and former editor of Science Today magazine.