My India 17- 1950-55

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In our childhood-home there was only one 'working' mirror at any point of time. That was a framed 'Table-Stood-up Affair', with a slanting and foldable back-stand. Its average life was about a couple of months, since it had to daily withstand seven female pairs of hands for their make-up and of my father for trimming his fancy mustache. Some kid or the other would drop it on the floor and the debris would be my property (since I had no use for 'working' mirrors).

As a matter of rule, it cracked into at least a dozen pieces of various sizes, ranging from a squarish 4" X 4" to a hexagonal miniature hardly 1" across. I preserved them in my toolkit and used to play with them all the time, in particular, wondering at the seven rainbow colors produced by their cracked edges, and fiddling with the shining red coating at the back (they called it mercury, but I doubt it).

My mother was and still is (at 88) a devotee of the Sun-God (my name is 'Prabhakar'). And she wouldn't partake any meal unless she had a look at the Sun going out the veranda, folding her hands up in salute and reciting 'Aditya Hridayam'. Since our Village in Southern AP was ever flooded with sunshine, there were hardly a couple of days per year when the entire day was Sunless. During the rainy season, it was the pleasant duty of her 7 kids to look out for the Sun and report His hide-and-seek with the clouds and drag her out into the open so she could pray and eat her lunch.

Once she fell down chasing away a monkey that invaded her kitchen and invited himself to a bunch of bananas. And fractured her leg. So, she was laid up (or down?) for six weeks unable to come out to view the Sun and pray. So, it fell to me to cast a reflected image of the Sun on the Wall of our Hall, using the mirror bits in my tool kit; something which even otherwise I enjoyed doing by way of play. This was about the first time when 'play' and 'duty' coincided happily (The 40 years at KGP was all 'play' with Physics doubling as 'Teaching & Research' Duties).

While playing with the mirrors and their reflected image of the Sun on the Wall, I discovered a strange thing which I couldn't follow why:

When I used the squarish 'big' piece of the mirror, the reflected image on the Wall was of the mirror (projected square). But when I used the 'tiny' bits, whatever their shape (hexagonal, triangular, trapezoidal etc), the reflected image on the Wall was always the perfectly circular (projected) image of the Sun.

I still remember my dismay.

Then there was this 'Touring Talkies' which pitched its Tarpaulin Tent for about 3 months or so every year in our Village before un-pegging it and relocating itself in a neighboring village. We kids used to go for the afternoon Matinee Show which had the subsidized rate of 2 Annas (1/8 th of a Rupee) for a 3-hour bonanza.

The 'Walls' of the tent were full of holes of all sizes and shapes. As the show starts, the 'doors' were all shut after everyone was in and seated on the floor (bringing their own mats), and the Cinema hall was darkened suitably so we can view the Movie projected by 'magic lanterns' and 'spinning reels'.

Since the Tent was by the roadside, as and when any cycle, bus, or cart used to pass by on the road outside in the Western sinking Sun, their reflected (sacttered)sunlight used to fall on the vertical Tarpaulin Walls of the Tent with its holes. And their moving inverted images used to be perfectly cast on the opposite side of the Tent Wall acting as a Screen. That was a bonus 'side-show'.

Wonderful that an oblong 'tear' in the Wall casts a perfect 'image' of a running bus on the road!

When my son was in his Class VII, their Science Book had this silly drawing of a 'Pin-Hole Camera' showing a really tiny hole and a screen casting an inverted image of a man with just 3 rays. So, I waned to investigate this topic further for the 'Science is Fun' Project for my son.

We entered our bedroom one night, shut all the doors and windows to make it a 'Dark Room' with a bulb on. We lit a candle giving its typical long tapering flame with its point upwards. We took a cardboard in which we can punch a hole with a screw driver, and placed it about 2 feet from the candle. This was our pin-hole. We then took a black Drawing Sheet as the Screen of our Camera. We at once found that if the hole is really tiny, the light allowed is so faint that one can't get any image at all. So, we punched bigger and bigger holes till enough light enters and the image on the black screen can be nicely seen when the electric bulb is switched off.

Here are our findings:

When the 'Screen' is next to the pin-hole in the sheet, the inverted image is that of the pin-hole (not of the candle flame).

As we moved the Screen gradually away from the pin-hole Sheet, the image gets distorted continuously and goes over to the perfect (aberrationless) beautiful inverted image of the candle 'flame' with its tip downwards and dancing as the flame does in the residual air currents.

I worked out the transition.

Result: Whether the Image is that of the Pin-Hole or the 'Object' depends on the ratio of the solid angle subtended by the Object at the Hole to the solid angle subtended by the Hole at the Screen.

Talking of solid angles, my son was given this challenging unsolved Project:

"Everyone knows that a 'Protractor' measures the 'angle' subtended by an arc.

Invent a Device that measures the Solid Angle subtended by a far-off Object at a point".

We sort of 'did' it.

Any takers?

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We had Aniket & Pratik with their families for lunch today.

In all, many KGPians (me, my son, Aniket, Pratik) and their families.

As usual, I didn't let anyone else talk.

And Aniket wondered as usual, where I get the 'chatter-box' energy from at my age.

Answer: Pent-up (stored) Energy over 5 long years.


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